Awk

Awk is a base Linux & FreeBSD command for stripping out data.

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 Use "tr" instead. tr -d \r 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 '/./'

Reference

 * http://www.student.northpark.edu/pemente/awk/awk1line.txt