天行健，君子以自强不息

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 <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 ‘/./‘