Awk Command
From Luke Jackson
| Revision as of 07:05, 19 January 2021 (edit) Ljackson (Talk | contribs) (→Mac OS X convert text from stdin bash command line into postscript pdf) ← Previous diff |
Current revision (07:06, 19 January 2021) (edit) Ljackson (Talk | contribs) (→Mac OS X convert text from stdin bash command line into postscript pdf) |
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| Solved documented xmlstarlet bug unescaping "" ;" using sed after first unescape, double unescape necessary due to html download of xml content, change in parsing results in less favorable line breaks. Adjusted awk to concatenate on all lines and then rely on sed to add newlines back in on line ending punctuation (!?.), sed cleanup to address awk inserted spaces | Solved documented xmlstarlet bug unescaping "" ;" using sed after first unescape, double unescape necessary due to html download of xml content, change in parsing results in less favorable line breaks. Adjusted awk to concatenate on all lines and then rely on sed to add newlines back in on line ending punctuation (!?.), sed cleanup to address awk inserted spaces | ||
| + | |||
| Direct Download M3U8 file playlist stream and convert into local MP4 video file | Direct Download M3U8 file playlist stream and convert into local MP4 video file | ||
Current revision
Usage
Unix: awk '/pattern/ {print "$1"}' # standard Unix shells
DOS/Win: awk '/pattern/ {print "$1"}' # okay for DJGPP compiled
awk "/pattern/ {print \"$1\"}" # required for Mingw32
Most of my experience comes from version of GNU awk (gawk) compiled for Win32. Note in particular that DJGPP compilations permit the awk script to follow Unix quoting syntax '/like/ {"this"}'. However, the user must know that single quotes under DOS/Windows do not protect the redirection arrows (<, >) nor do they protect pipes (|). Both are special symbols for the DOS/CMD command shell and their special meaning is ignored only if they are placed within "double quotes." Likewise, DOS/Win users must remember that the percent sign (%) is used to mark DOS/Win environment variables, so it must be doubled (%%) to yield a single percent sign visible to awk.
If I am sure that a script will NOT need to be quoted in Unix, DOS, or CMD, then I normally omit the quote marks. If an example is peculiar to GNU awk, the command 'gawk' will be used. Please notify me if you find errors or new commands to add to this list (total length under 65 characters). I usually try to put the shortest script first.
File Spacing
# double space a file
awk '1;{print ""}'
awk 'BEGIN{ORS="\n\n"};1'
# double space a file which already has blank lines in it. Output file
# should contain no more than one blank line between lines of text.
# NOTE: On Unix systems, DOS lines which have only CRLF (\r\n) are
# often treated as non-blank, and thus 'NF' alone will return TRUE.
awk 'NF{print $0 "\n"}'
# triple space a file
awk '1;{print "\n"}'
Numbering and Calculations
# precede each line by its line number FOR THAT FILE (left alignment).
# Using a tab (\t) instead of space will preserve margins.
awk '{print FNR "\t" $0}' files*
# precede each line by its line number FOR ALL FILES TOGETHER, with tab.
awk '{print NR "\t" $0}' files*
# number each line of a file (number on left, right-aligned)
# Double the percent signs if typing from the DOS command prompt.
awk '{printf("%5d : %s\n", NR,$0)}'
# number each line of file, but only print numbers if line is not blank
# Remember caveats about Unix treatment of \r (mentioned above)
awk 'NF{$0=++a " :" $0};{print}'
awk '{print (NF? ++a " :" :"") $0}'
# count lines (emulates "wc -l")
awk 'END{print NR}'
# print the sums of the fields of every line
awk '{s=0; for (i=1; i<=NF; i++) s=s+$i; print s}'
# add all fields in all lines and print the sum
awk '{for (i=1; i<=NF; i++) s=s+$i}; END{print s}'
# print every line after replacing each field with its absolute value
awk '{for (i=1; i<=NF; i++) if ($i < 0) $i = -$i; print }'
awk '{for (i=1; i<=NF; i++) $i = ($i < 0) ? -$i : $i; print }'
# print the total number of fields ("words") in all lines
awk '{ total = total + NF }; END {print total}' file
# print the total number of lines that contain "Beth"
awk '/Beth/{n++}; END {print n+0}' file
# print the largest first field and the line that contains it
# Intended for finding the longest string in field #1
awk '$1 > max {max=$1; maxline=$0}; END{ print max, maxline}'
# print the number of fields in each line, followed by the line
awk '{ print NF ":" $0 } '
# print the last field of each line
awk '{ print $NF }'
# print the last field of the last line
awk '{ field = $NF }; END{ print field }'
# print every line with more than 4 fields awk 'NF > 4'
# print every line where the value of the last field is > 4 awk '$NF > 4'
Text Conversion and Substitution
# IN UNIX ENVIRONMENT: convert DOS newlines (CR/LF) to Unix format
awk '{sub(/\r$/,"");print}' # assumes EACH line ends with Ctrl-M
# IN UNIX ENVIRONMENT: convert Unix newlines (LF) to DOS format
awk '{sub(/$/,"\r");print}
# IN DOS ENVIRONMENT: convert Unix newlines (LF) to DOS format awk 1
# IN DOS ENVIRONMENT: convert DOS newlines (CR/LF) to Unix format # Cannot be done with DOS versions of awk, other than gawk: gawk -v BINMODE="w" '1' infile >outfile
Remove newline char at end of line
awk '{printf("%s ",$0)}'
# Use "tr" instead. tr -d \r <infile >outfile # GNU tr version 1.22 or higher
# delete leading whitespace (spaces, tabs) from front of each line
# aligns all text flush left
awk '{sub(/^[ \t]+/, ""); print}'
# delete trailing whitespace (spaces, tabs) from end of each line
awk '{sub(/[ \t]+$/, "");print}'
# delete BOTH leading and trailing whitespace from each line
awk '{gsub(/^[ \t]+|[ \t]+$/,"");print}'
awk '{$1=$1;print}' # also removes extra space between fields
# insert 5 blank spaces at beginning of each line (make page offset)
awk '{sub(/^/, " ");print}'
# align all text flush right on a 79-column width
awk '{printf "%79s\n", $0}' file*
# center all text on a 79-character width
awk '{l=length();s=int((79-l)/2); printf "%"(s+l)"s\n",$0}' file*
# substitute (find and replace) "foo" with "bar" on each line
awk '{sub(/foo/,"bar");print}' # replaces only 1st instance
gawk '{$0=gensub(/foo/,"bar",4);print}' # replaces only 4th instance
awk '{gsub(/foo/,"bar");print}' # replaces ALL instances in a line
# substitute "foo" with "bar" ONLY for lines which contain "baz"
awk '/baz/{gsub(/foo/, "bar")};{print}'
# substitute "foo" with "bar" EXCEPT for lines which contain "baz"
awk '!/baz/{gsub(/foo/, "bar")};{print}'
# change "scarlet" or "ruby" or "puce" to "red"
awk '{gsub(/scarlet|ruby|puce/, "red"); print}'
# reverse order of lines (emulates "tac")
awk '{a[i++]=$0} END {for (j=i-1; j>=0;) print a[j--] }' file*
# if a line ends with a backslash, append the next line to it
# (fails if there are multiple lines ending with backslash...)
awk '/\\$/ {sub(/\\$/,""); getline t; print $0 t; next}; 1' file*
# print and sort the login names of all users
awk -F ":" '{ print $1 | "sort" }' /etc/passwd
# print the first 2 fields, in opposite order, of every line
awk '{print $2, $1}' file
# switch the first 2 fields of every line
awk '{temp = $1; $1 = $2; $2 = temp}' file
# print every line, deleting the second field of that line
awk '{ $2 = ""; print }'
# print in reverse order the fields of every line
awk '{for (i=NF; i>0; i--) printf("%s ",i);printf ("\n")}' file
# remove duplicate, consecutive lines (emulates "uniq")
awk 'a !~ $0; {a=$0}'
# remove duplicate, nonconsecutive lines
awk '! a[$0]++' # most concise script
awk '!($0 in a) {a[$0];print}' # most efficient script
# concatenate every 5 lines of input, using a comma separator # between fields awk 'ORS=%NR%5?",":"\n"' file
Selective Printing of Certain Lines
# print first 10 lines of file (emulates behavior of "head") awk 'NR < 11'
# print first line of file (emulates "head -1")
awk 'NR>1{exit};1'
# print the last 2 lines of a file (emulates "tail -2")
awk '{y=x "\n" $0; x=$0};END{print y}'
# print the last line of a file (emulates "tail -1")
awk 'END{print}'
# print only lines which match regular expression (emulates "grep") awk '/regex/'
# print only lines which do NOT match regex (emulates "grep -v") awk '!/regex/'
# print the line immediately before a regex, but not the line
# containing the regex
awk '/regex/{print x};{x=$0}'
awk '/regex/{print (x=="" ? "match on line 1" : x)};{x=$0}'
# print the line immediately after a regex, but not the line
# containing the regex
awk '/regex/{getline;print}'
# grep for AAA and BBB and CCC (in any order) awk '/AAA/; /BBB/; /CCC/'
# grep for AAA and BBB and CCC (in that order) awk '/AAA.*BBB.*CCC/'
# print only lines of 65 characters or longer awk 'length > 64'
# print only lines of less than 65 characters awk 'length < 64'
# print section of file from regular expression to end of file awk '/regex/,0' awk '/regex/,EOF'
# print section of file based on line numbers (lines 8-12, inclusive) awk 'NR==8,NR==12'
# print line number 52
awk 'NR==52'
awk 'NR==52 {print;exit}' # more efficient on large files
# print section of file between two regular expressions (inclusive) awk '/Iowa/,/Montana/' # case sensitive
Selective Deletion of Certain Lines
# delete ALL blank lines from a file (same as "grep '.' ") awk NF awk '/./'
Examples
Parse Hyperlink Text between href tags
cat untitled.txt | awk -F'[<|>]' '{print $3}' | sed 's/^ *//;s/ *$//' | tr -s "\r\n" ","
Fetch Printer Report and E-Mail
wget -O- http://192.168.1.12/start/StatPtr1.htm | grep 'sLabel\[' | head -n 6 | awk -F'"' '{ print $2": "$4 }' | mail -s 'Kyrocera MS-4000DN Printer Report' email@email.com
Clean Up Jpeg Files Based on Date
Convert unix timestamp from filename to folder path based on date:
ls -1 *.jpg | awk -F _ '{print $2}' | sed 's/[^[:digit:]]//g' | utimecam
Batch rename files
Rename file including only the second field:
ls -1 | awk -F - '{print("mv \"" $0"\""" \""$2"\"")}' | /bin/sh
Rename file excluding only the first field:
ls -1 | awk -F _ '{str=$2;for(i=3;i<=NF;++i) str=str FS $i; print("mv " $0 " "str)}' | /bin/sh
Bulk Rename files separated by - character, including spaces in file names with bash
ls -1 | awk -F - '{str=$2;for(i=3;i<=NF;++i) str=str FS $i; print("mv " "\""$0"\"" " \""str"\"")}' | /bin/sh
Fetch local ip and return 3rd octet (Mac OS X)
ifconfig en0 | grep 'broadcast' | awk '{print $2}' | awk -F . '{print $3}'
ifconfig | grep -Eo '[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}' | awk -F . '$1 != 127 && $1 !=255 && $4 < 255 {print $3}'
Total list of numbers
awk 'BEGIN{total=0} {total += $1} END{print total}'
Bulk Rename SQL Tables
awk -F'_' '{t=$0; for(i=n;i<=NF;i++)$(i-(n-1))=$i;NF=NF-(n-1);print "RENAME TABLE `database`.`"t"` TO `database`.`user_"$0"`;" }' OFS='_' n=4 FILE_EXT
awk -F'_' '{t=$0; for(i=n;i<=NF;i++)$(i-(n-1))=$i;NF=NF-(n-1);print "ALTER TABLE `database`.`user_"$0"` DEFAULT CHARACTER SET utf8 COLLATE utf8_general_ci;" }' OFS='_' n=4 FILE_EXT
awk -F'_' '{t=$0; for(i=n;i<=NF;i++)$(i-(n-1))=$i;NF=NF-(n-1);print "ALTER TABLE `database`.`user_"$0"` ENGINE = InnoDB;" }' OFS='_' n=4 FILE_EXT
Sum Column of Numbers
Earned Points
pbpaste | tr '\t' ' ' | grep -E '[0-9\.]{2,}$' | cut -d' ' -f 7 | awk '{s+=$1} END {print s}'
Total Points
pbpaste | tr '\t' ' ' | grep -E '^ [0-9\.][^\.%]{2,}' | cut -d' ' -f 2 | awk '{s+=$1} END {print s}'
Sum Ledger
pbpaste | cut -f 5 | sed 's/[^0-9\.]//g' | awk '{ sum+=$1} END {print sum}'
Convert XML to MySQL
Revers Line Order For Alter Table
awk -F'[<>]' '{a[i++]=$2} END {for (j=i-1; j>=0;) print "ALTER TABLE `user_prd_ddd_setup_types` ADD `"tolower(a[j--])"` VARCHAR( 30 ) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL AFTER `name`;"}' tmp.xml
Match INT(10)
awk -F'[<>]' '{print $2","$3}' tmp.xml | awk -F',' '$2 ~ /^[0-9]+$/ {print "ALTER TABLE `user_prd_ddd_setup_types` CHANGE `"tolower($1)"` `"tolower($1)"` INT( 10 ) UNSIGNED NOT NULL DEFAULT '0';"}'
Match FLOAT(6,3)
awk -F'[<>]' '{print $2","$3}' tmp.xml | awk -F',' '$2 ~ /^[0-9]+[\.]+[^\.[:alpha:]]*$/ {print "ALTER TABLE `user_prd_ddd_setup_types` CHANGE `"tolower($1)"` `"tolower($1)"` FLOAT( 6,3 ) UNSIGNED NOT NULL DEFAULT '0';"}'
Match TINYINT(1)
awk -F'[<>]' '{print $2","$3}' tmp.xml | awk -F',' '$2 ~ /^(true|false)$/ {print "ALTER TABLE `user_prd_ddd_setup_types` CHANGE `"tolower($1)"` `"tolower($1)"` TINYINT( 1 ) UNSIGNED NOT NULL DEFAULT '0';"}'
Add Prefix AND/OR Suffix to String (Convert Windows Line Break)
cat A1000.kst | sed 's/^ *//;s/ *$//' | sed $'s/\r$//' | awk -v PRE='$file_body .= "' -v SUF='"."\\n";' '{ $0=PRE$0SUF; print ($0) }'
cat file.txt | tr -d "\r" | awk '{print "$file_body .= \""$0"\".\"\\n\";"}'
pbpaste | cut -f 2- | awk '{print "* "$0"\n"}' | pbcopy
If Statements (if field length is...)
Export only src or href from course data
grep -H 'ENV = ' video-lectures-lesson-* | tr '"' '\n' | awk -F'[: ]' '{ if ($4 == "ENV" && $1 != prefix) prefix=$1; print prefix","$0}'| sed -n '/src/{n;p;}' | sed 's/\\//g;s/"//g'
Convert to wget string with awk and execute with bash
grep -H 'ENV = ' video-lectures-lesson-* | tr '"' '\n' | awk -F'[: ]' '{ if ($4 == "ENV" && $1 != prefix) prefix=$1; split(prefix,s,"[\-\.]"); print s[3]"-"s[4]","$0}'| sed -n '/src/{n;p;}' | sed 's/\\//g;s/"//g' | grep mp4 | awk -F',' '{ split($2,s,"[\/]"); print "wget "$2" -O "$1"-"s[5]}' | /bin/sh
Export only contacts from google
cat contacts.csv | cut -d',' -f 1-3 | awk -F ',' '{ if (length($3) > 1 && length($2) == 0) print $0}'
Replace values based on last value of specific field
awk -F'[: ]' '{ if ($4 == "ENV" && $1 != prefix) prefix=$1; print prefix","$0}'
Export captions
cat 2505476419001_captions | grep '^[^0-9]' | awk '{ if (substr($0, length($0), 1)==",") print ""$0"#"; else print $0;}'
cat 2505476419001_captions | grep '^[^0-9]' | awk '/[^.]$/ { printf("%s ", $0); next } 1'
Prefix the date from XML data to create comma separated values and grep on specific values
pbpaste | grep -H '<' *.xml | awk -F'[>:.<]' '{ if ($4 == "Date" && $5 != prefix) prefix=$5; print prefix","$1","$4","$5}' | grep 'Date\|RightTablePrints\|LeftTablePrints\|TotalTablesPrints\|WhiteBridgePrints\|ColorBridgePrints'
Prefix the date from XML data to create comma separated values
pbpaste | awk '{ if ($1 == "PDF") prefix="+"; else prefix=""; print $0prefix}' | tr '\n' ',' | tr '+' '\n'
Safe String, remove all non alphanumerical chars and format for filenames
pbpaste | sed '/^$/d; s/^ *//; s/ *$//' | tr -dc '[:alnum:]\. \-\n\r' | awk '{gsub(/ /,"."); print tolower($0)}'
Escape Single Quotes and build Python Dict from CSV list
pbpaste | tr '\r\n' '\n' | awk -F',' '{print "'\''"$1"'\'': {'\''desc'\'': '\''"$2"'\'', '\''price'\'':"$3", '\''type'\'': '\''"$4"'\'', '\''avail'\'': "$5"},"}'
List of numbers padded with zeros separated by string
seq -f %02g 0 24 | awk 'BEGIN{ORS="'\'','\''"} {print ""$0""}'
Mac OS X convert text from stdin bash command line into postscript pdf
pbpaste | enscript --word-wrap -p - | pstopdf -i -o ~/Downloads/tmp.pdf
Closed Captions filtered through REGEX with string chunks concatenated into sentences (Carriage Return Safe)
cat file.txt | sed "s/[”“]/\"/g;s/[’]/'/g" | sed 's/\r$//;s/[^0-9A-Za-z [:punct:]]//g;/^ $/d;s/^ *//;s/ *$//;' | grep -E '^[^0-9]{2,}' | awk '/[^.]$/ { printf("%s ", $0); next } 1' | enscript --word-wrap -p - | pstopdf -i -o ~/Downloads/Ch2_New_Belgium_Brewery.pdf
Youtube captions converted into PDF
curl-O https://www.youtube.com/api/timedtext?<query_string> | tr '>' '\n' | grep -E '^alpha:{1,}' | cut -d'<' -f 1
cat timedtext.xml | tr '>' '\n' | sed '/^ $/d;s/^ *//;s/ *$//;' | grep -E '^[[:alnum:]\.,]{1,}' | cut -d'<' -f 1 | awk '/[^.]$/ { printf("%s ", $0); next } 1' | pbcopy
Revised 2021.01.18
xmlstarlet sel -t -v "//text" timedtext.xml | xmlstarlet unesc | xmlstarlet unesc | awk '/[^.]$/ { printf("%s ", $0); next } 1' | enscript --word-wrap -p - | pstopdf -i -o ~/Downloads/trump.pdf
Odd artifacts with HTML and XML encoding that forcing the unescape command to need to be ran twice...still not sure about "
Revised 2021.01.19
xmlstarlet sel -t -v "//text" timedtext.xml | xmlstarlet unesc | sed 's/"/\"/g;' | xmlstarlet unesc | awk '{ printf("%s ", $0); next } 1' | sed 's/\([.!?]\)/\1\'$'\n/g' | sed '/^ $/d; s/^ *//; s/ *$//;'
xmlstarlet sel -t -v "//text" timedtext.xml | xmlstarlet unesc | sed 's/"/\"/g;' | xmlstarlet unesc | awk '{ printf("%s ", $0); next } 1' | sed 's/\([.!?]\)/\1\'$'\n/g' | sed '/^ $/d; s/^ *//; s/ *$//;' | enscript --word-wrap -p - | pstopdf -i -o ~/Downloads/trump3.pdf
Solved documented xmlstarlet bug unescaping "" ;" using sed after first unescape, double unescape necessary due to html download of xml content, change in parsing results in less favorable line breaks. Adjusted awk to concatenate on all lines and then rely on sed to add newlines back in on line ending punctuation (!?.), sed cleanup to address awk inserted spaces
Direct Download M3U8 file playlist stream and convert into local MP4 video file
echo "Enter m3u8 link:";read link;echo "Enter output filename:";read filename;ffmpeg -i "$link" -bsf:a aac_adtstoasc -vcodec copy -c copy -crf 23 $filename.mp4
-bsf:a aac_adtstoasc
bsf = (bit stream filter)
use aac_adtstoasc bsf for a audio streams, this is need if .m3u8 file consists with .ts files and output is .mp4
reference https://ffmpeg.org/ffmpeg-bitstream-filters.html#aac_005fadtstoasc
-c copy -vcodec copy
skip codec (encode and decode), just demux and mux
I guess .ts and .mp4, for video stream, they are both H.264 codec, just guess.
reference https://ffmpeg.org/ffmpeg.html#Stream-copy
-crf 50
reference https://trac.ffmpeg.org/wiki/Encode/H.264#CRFExample
the example shows -c:a copy did not re-encode, guess this option is not needed here.
And 0 is lossless, 23 is the default, and 51 is worst quality possible 😢
https://gist.github.com/tzmartin/fb1f4a8e95ef5fb79596bd4719671b5d
Convert Sorted 'du -k' into Human Readable (Megabytes)
du -d 1 -k | sort -nr | awk '$1 > 10240 {print $1 / 1024 $2}'
Parse Backlog Tool
Exclamation Mark Reverses Order
pbpaste | awk -F'%' '/[0-9]{6,}\-[0-9]{6,}|([0-9]{4}\-[0-9]{2}\-[0-9]{2} [0-9]{2}\:[0-9]{2}\:[0-9]{2})\([0-9]+ h\)/ {print $0}' | awk '!(NR%2){print p","$0}{p=$0}'
pbpaste | awk -F'%' '/[0-9]{6,}\-[0-9]{6,}|([0-9]{4}\-[0-9]{2}\-[0-9]{2} [0-9]{2}\:[0-9]{2}\:[0-9]{2})\([0-9]+ h\)/ {print $0}' | awk '(NR%2){print p","$0}{p=$0}'
pbpaste | awk '/[0-9]{6,}\-[0-9]{6,}/ {print x","$0};{x=$0}'
If field two is equal to nothing, do nothing, else return line
"C:\Program Files (x86)\GnuWin32\bin\awk.exe" -F"[,]" "{ if ($2 ==\"\") print \"~,\"$1; else print \",\"$2; }"
Sources
Special thanks to Peter S. Tillier for helping me with the first release of this FAQ file.
For additional syntax instructions, including the way to apply editing commands from a disk file instead of the command line, consult:
"sed & awk, 2nd Edition," by Dale Dougherty and Arnold Robbins
O'Reilly, 1997
"UNIX Text Processing," by Dale Dougherty and Tim O'Reilly
Hayden Books, 1987
"Effective awk Programming, 3rd Edition." by Arnold Robbins
O'Reilly, 2001
To fully exploit the power of awk, one must understand "regular expressions." For detailed discussion of regular expressions, see "Mastering Regular Expressions, 2d edition" by Jeffrey Friedl
(O'Reilly, 2002).
The manual ("man") pages on Unix systems may be helpful (try "man awk", "man nawk", "man regexp", or the section on regular expressions in "man ed"), but man pages are notoriously difficult. They are not written to teach awk use or regexps to first-time users, but as a reference text for those already acquainted with these tools.
USE OF '\t' IN awk SCRIPTS: For clarity in documentation, we have used the expression '\t' to indicate a tab character (0x09) in the scripts. All versions of awk, even the UNIX System 7 version should recognize the '\t' abbreviation.
Convert Sorted 'du -k' into Human Readable (Megabytes)
du -d 1 -k | sort -nr | awk '$1 > 10240 {print $1 / 1024 $2}'
Parse Backlog Tool
Exclamation Mark Reverses Order
pbpaste | awk -F'%' '/[0-9]{6,}\-[0-9]{6,}|([0-9]{4}\-[0-9]{2}\-[0-9]{2} [0-9]{2}\:[0-9]{2}\:[0-9]{2})\([0-9]+ h\)/ {print $0}' | awk '!(NR%2){print p","$0}{p=$0}'
pbpaste | awk -F'%' '/[0-9]{6,}\-[0-9]{6,}|([0-9]{4}\-[0-9]{2}\-[0-9]{2} [0-9]{2}\:[0-9]{2}\:[0-9]{2})\([0-9]+ h\)/ {print $0}' | awk '(NR%2){print p","$0}{p=$0}'
pbpaste | awk '/[0-9]{6,}\-[0-9]{6,}/ {print x","$0};{x=$0}'
If field two is equal to nothing, do nothing, else return line
"C:\Program Files (x86)\GnuWin32\bin\awk.exe" -F"[,]" "{ if ($2 ==\"\") print \"~,\"$1; else print \",\"$2; }"
Sources
Special thanks to Peter S. Tillier for helping me with the first release of this FAQ file.
For additional syntax instructions, including the way to apply editing commands from a disk file instead of the command line, consult:
"sed & awk, 2nd Edition," by Dale Dougherty and Arnold Robbins
O'Reilly, 1997
"UNIX Text Processing," by Dale Dougherty and Tim O'Reilly
Hayden Books, 1987
"Effective awk Programming, 3rd Edition." by Arnold Robbins
O'Reilly, 2001
To fully exploit the power of awk, one must understand "regular expressions." For detailed discussion of regular expressions, see "Mastering Regular Expressions, 2d edition" by Jeffrey Friedl
(O'Reilly, 2002).
The manual ("man") pages on Unix systems may be helpful (try "man awk", "man nawk", "man regexp", or the section on regular expressions in "man ed"), but man pages are notoriously difficult. They are not written to teach awk use or regexps to first-time users, but as a reference text for those already acquainted with these tools.
USE OF '\t' IN awk SCRIPTS: For clarity in documentation, we have used the expression '\t' to indicate a tab character (0x09) in the scripts. All versions of awk, even the UNIX System 7 version should recognize the '\t' abbreviation.