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Editorial Team
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Asked: 2026-05-15T11:39:57+00:00

Starting with a string of an unspecified length, I need to make it exactly

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Starting with a string of an unspecified length, I need to make it exactly 43 characters long (front-padded with zeroes). It is going to contain IP addresses and port numbers. Something like:

### BEFORE
# Unfortunately includes ':' colon
66.35.205.123.80-137.30.123.78.52172:
### AFTER
# Colon removed.
# Digits padded to three (3) and five (5) 
# characters (for IP address and port numbers, respectively)
066.035.005.123.00080-137.030.123.078.52172

This is similar to the output produced by tcpflow.

Programming in Bash. I can provide copy of script if required.
If it’s at all possible, it would be nice to use a bash built-in, for speed. Is printf suitable for this type of thing?

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1 Answer

  1. Editorial Team

    This uses IFS to split the address info into an array. Then printf saves the formatted result back into the original variable for further processing. Pure Bash – no external executables are used.

    addr='66.35.205.123.80-137.30.123.78.52172:'
saveIFS=$IFS
IFS='.-:'
arr=($addr)
IFS=$saveIFS
printf -v addr "%03d.%03d.%03d.%03d.%05d-%03d.%03d.%03d.%03d.%05d" ${arr[@]}
do_something "$addr"

    Edit:

    Without using an array:

    addr='66.35.205.123.80-137.30.123.78.52172:'
saveIFS=$IFS
IFS='.-:'
printf -v addr "%03d.%03d.%03d.%03d.%05d-%03d.%03d.%03d.%03d.%05d" $addr
IFS=$saveIFS
do_something "$addr"
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