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06-24-2016

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I see three alternatives:
1. Everything to a for loop

Code:

#!/bin/sh
if [ $# -gt 0 ]
then
  patterns="$@"
else
  patterns=`cat`
fi
set -f # no wildcard globbing for safety
for pattern in $patterns
do
  # loop code
  printf '%s\n' "$pattern"
done

If no argument is given, it loops over the words from stdin.
Unlike the following two solutions, where the while loop reads the lines from stdin.
2. Everything to a while loop (simpler than Don's solution)

Code:

#!/bin/sh
if [ $# -gt 0 ]
then
  printf '%s\n' "$@"
else
  cat
fi |
while IFS= read -r pattern
do
  # loop code
  printf '%s\n' "$pattern" 
done

3. separate for and while loops, common part in a function

Code:

#!/bin/sh
loop_code(){
   printf '%s\n' "$pattern"
}
if [ $# -gt 0 ]
then
  for pattern in "$@"
  do
    loop_code
  done
else
  while IFS= read -r pattern
  do
    loop_code
  done
fi

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