Shortest way to swap two files in bash

2015-03-10

An answer to this question on Stack Overflow.

Question

Can two files be swapped in bash?

Or, can they be swapped in a shorter way than this:

cp old tmp
cp curr old
cp tmp curr
rm tmp

Answer

This is what I use as a command on my system ($HOME/bin/swapfiles). I think it is relatively resilient to badness.

#!/bin/bash
if [ "$#" -ne 2 ]; then
  me=`basename $0`
  echo "Syntax: $me <FILE 1> <FILE 2>"
  exit -1
fi
if [ ! -f $1 ]; then
  echo "File '$1' does not exist!"
fi
if [ ! -f $2 ]; then
  echo "File '$2' does not exist!"
fi
if [[ ! -f $1 || ! -f $2 ]]; then
  exit -1
fi
tmpfile=$(mktemp $(dirname "$1")/XXXXXX)
if [ ! -f $tmpfile ]; then
  echo "Could not create temporary intermediate file!"
  exit -1
fi
# move files taking into account if mv fails
mv "$1" "$tmpfile" && mv "$2" "$1" && mv "$tmpfile" "$2"