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VimleshS/cols.txt

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Created January 16, 2019 12:46
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  1. @0 0 created this gist Apr 30, 2013.
    4 changes: 4 additions & 0 deletions cols.txt
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    Original file line number Diff line number Diff line change
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    abc 1 2 3
    def 4 5 6
    ga 7 9 10
    hij 1 5 99
    171 changes: 171 additions & 0 deletions tutorial.md
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    # Example input

    $ cat cols.txt
    abc 1 2 3
    def 4 5 6
    ga 7 9 10
    hij 1 5 99

    The columns are separated by tabs, but any whitespace will do for awk.


    # Matching lines

    Remember that "numbers" are just character strings!


    ## Regular expressions

    An "a" in the first column:

    $ awk '$1 ~ /a/' cols.txt
    abc 1 2 3
    ga 7 9 10

    An "a" at the start of the first column:

    $ awk '$1 ~ /^a/' cols.txt
    abc 1 2 3

    A "9" in the fourth column:

    $ awk '$4 ~ /9/' cols.txt
    hij 1 5 99

    A "9" in any column:

    $ awk '/9/' cols.txt
    ga 7 9 10
    hij 1 5 99

    A "99" in any column:

    $ awk '/99/' cols.txt
    hij 1 5 99


    ## Exact string matches

    Second column must be exactly "1":

    $ awk '$2 == "1"' cols.txt
    abc 1 2 3
    hij 1 5 99

    Third column must be exactly "5":

    $ awk '$3 == "5"' cols.txt
    def 4 5 6
    hij 1 5 99

    Fourth column must be exactly "9":

    $ awk '$4 == "9"' cols.txt

    Fourth column must be exactly "99":

    $ awk '$4 == "99"' cols.txt
    hij 1 5 99


    # Extracting output

    Where the match occurs, print the entire line:

    $ awk '$2 == "1" { print $0 }' cols.txt
    abc 1 2 3
    hij 1 5 99

    ... print the fourth column:

    $ awk '$2 == "1" { print $4 }' cols.txt
    3
    99

    ... print the third and fourth columns:

    $ awk '$2 == "1" { print $3 $4 }' cols.txt
    23
    599

    ... separated by a space:

    $ awk '$2 == "1" { print $3, $4 }' cols.txt
    2 3
    5 99

    ... separated by a tab:

    $ awk '$2 == "1" { print $3 "\t" $4 }' cols.txt
    2 3
    5 99


    # Arithmetic

    Digit strings can also be treated as numbers by awk.

    ## Operations

    Add values:

    $ awk '{ print 2 + 2 }' cols.txt
    4
    4
    4
    4

    ... once:

    $ awk 'BEGIN { print 2 + 2 }' cols.txt
    4

    Add columns:

    $ awk '{ print $2 + $3 + $4 }' cols.txt
    6
    15
    26
    105

    Calculate means, even if they are non-integer:

    $ awk '{ print ($2 + $3 + $4) / 3 }' cols.txt
    2
    5
    8.66667
    35


    ## Running sums

    Sum the values in the fourth column:

    $ awk '{ sum += $4 } END { print sum }' cols.txt
    118

    ... if the second column matches:

    $ awk '$2 == "1" { sum += $4 } END { print sum }' cols.txt
    102

    ... and also print the values used:

    $ awk '$2 == "1" { print $4; sum += $4 } END { print sum }' cols.txt
    3
    99
    102

    ... and also print the rows used:

    $ awk '$2 == "1" { print; sum += $4 } END { print sum }' cols.txt
    abc 1 2 3
    hij 1 5 99
    102

    ... and use an initial value:

    $ awk 'BEGIN { sum = 1000 } $2 == "1" { print; sum += $4 } END { print sum }' cols.txt
    abc 1 2 3
    hij 1 5 99
    1102