The following script works fine in one of my machines, printing 1 then 2:
#!/bin/sh
echo "1"
shift
echo "2"
On another machine, however, it produces the following output:
1
./script.sh: 4: shift: can't shift that many
man shift does not help (No manual entry for shift).
What is that error, why is it happening, and how can I fix it?
1 Answer
What is shift: it is a shell built-in that works as follows (adapted from TLDP):
The shift command takes one argument, a number (if not present, it is assumed to be 1). The positional parameters (e.g. command arguments) are shifted to the left by this number, N. The positional parameters from N+1 to $# are renamed to variable names from $1 to $# - N+1.
Often you make a loop in which you process one or more arguments, then you call shift to "forget" them and loop again to process the following ones.
Error cause:
The error comes from the fact that some shells (but not all) detect when there are not enough arguments for shift. In particular, dash considers it a fatal error.
Possible solutions:
Test if there are enough remaining arguments:
if [ "$#" -gt 0 ]; then shift; fiAdd a conditional argument:
shift $(( $# > 0 ? 1 : 0 ))
