Linux command: awk

Comand line text processing

Examples:

awk -F, '{print NR, length($0)}' filename.txt  #print line number and line length
awk '{print FILENAME " " length($0)}' */PRF* | uniq

awk 'BEGIN { FS = "," } ; { print $2 }'  #Specify separator ',' can be done with -F too.
awk -F"," '$2~/^ABC$/' file  #Find in a csv second field = ABC

Print from 3rd field till end

awk '{              \
       for (i = 3; i <= NF; i++) {   \
          printf("%s ", $i);         \
       }                             \
       printf("\n") }'

Print with condition

awk '{if ($3 =="" || $4 == "" || $5 == "") print "Some score for the student",$1,"is missing";'}' student-marks

Print if value

$ echo "a b c d" | awk '($4){print "yes"}'
yes
$ echo "a b c d" | awk '($14){print "yes"}' ## prints nothing, no $14
$ echo "a b c 0" | awk '($4){print "yes"}' ## prints nothing, $4 is 0

Print columns as lines

ls -lR | awk '{for(x=1;$x;++x) print $x}'
awk '{for(x=1;$x;x++)print $x}' 
          ___ __ ___
           |   |  |
           |   |  |-----> increment x by 1 at the end of each loop.
           |   |--------> run the loop as long as there is a field number x
           |------------> initialize x to 1