mjhjmtu

I've got a bash script I'd like to loop over the lines in stdin, or loop over each argument passed in.

Is there a clean way to write this so I don't have to have 2 loops?

#!/bin/bash

# if we have command line args... 
if [ -t 0 ]
then
 # loop over arguments
 for arg in "$@" 
 do
 # process each argument
 done
else
 # loop over lines from stdin
 while IFS= read -r line; do
 # process each line
 done
fi

EDIT: I'm looking for a generic solution that just uses a single loop, as I find I want to do this quite often, but have always wrote out 2 loops and then called a function instead. So maybe something that turns stdin into an array, so I could use a single loop instead?

Create data for your while read loop:

#!/bin/sh

if [ "$#" -gt 0 ]; then
 # We have command line arguments.
 # Output them with newlines in-between.
 printf '%sn' "$@"
else
 # No command line arguments.
 # Just pass stdin on.
 cat
fi |
while IFS= read -r; do
 printf 'Got "%s"n' "$REPLY"
done

Note that your concat example can be done with the while read loop replaced by tr 'n' ',' or similar.

Also, the -t test says nothing about whether you have command line arguments or not.

Alternatively, to process both command line arguments and standard input (in that order):

#!/bin/sh


 if [ "$#" -gt 0 ]; then
 # We have command line arguments.
 # Output them with newlines in-between.
 printf '%sn' "$@"
 fi

 if [ ! -t 0 ]; then
 # Pass stdin on.
 cat
 fi
 |
while IFS= read -r; do
 printf 'Got "%s"n' "$REPLY"
done

Or, using short-cut notation that some people seems to like:

#!/bin/sh


 [ "$#" -gt 0 ] && printf '%sn' "$@"
 [ ! -t 0 ] && cat
 |
while IFS= read -r; do
 printf 'Got "%s"n' "$REPLY"
done

With bash specifically, you could do:

if [ -t 0 ]; then
 args=("$@")
else
 readarray -t args
fi
for i in "$args[@]"; do
 ...
done