/contrib/famzah

The classical approach is:

RESULT="$(echo "$LINE"| awk '{print $1}')" # executes in a sub-shell 

Processing thousands of lines this way however fork()’s thousands of processes, which affects performance and makes your script CPU hungry.

Here is the effective solution which I found with my colleagues at work:

COLS=( $LINE ); # parses columns without executing a sub-shell
RESULT="${COLS[0]}"; # returns first column (0-based indexes)

Here is an example:

LINE="col0 col1  col2     col3  col4      " # white-space including tab chars
COLS=( $LINE ); # parses columns without executing a sub-shell

echo "${COLS[0]}"; # prints "col0"
echo "${COLS[1]}"; # prints "col1"
echo "${COLS[2]}"; # prints "col2"
echo "${COLS[3]}"; # prints "col3"
echo "${COLS[4]}"; # prints "col4"

If you want to split not by white-space but by any other character, you can temporarily change the IFS variable which determines how Bash recognizes fields and word boundaries.

This entry was posted on Sunday, February 17th, 2013 at 9:28 am and is filed under Development, Linux. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.