Using a plain ls | grep and/or ls dir/ | grep (with the trailing slash) is safe and predictable. Per POSIX, they would always output one entry per line since the output is piped (i.e. not output to a terminal). Both forms cannot confuse a directory with a file (as in ls dir | grep).
The relevant bit from POSIX:
The default format shall be to list one entry per line to standard output; the exceptions are to terminals or when one of the -C, -m, or -x options is specified.
Here's a snippet or screenshot that shows the problem:
#!/bin/sh
ls | grep
ls dir/ | grep
ls | cat
Here's what shellcheck currently says:
^-- [SC2010](https://www.shellcheck.net/wiki/SC2010) (warning): Don't use ls | grep. Use a glob or a for loop with a condition to allow non-alphanumeric filenames.
^-- [SC2012](https://www.shellcheck.net/wiki/SC2012) (info): Use find instead of ls to better handle non-alphanumeric filenames.
The warning also seems to be misleading. I don't believe ls has any issues with non-alphanumeric filenames when not outputting to a terminal (only newlines, and many things would break in that case, including find which is suggested). The warning should be changed to check for arguments not terminated with a slash, or at the very least allow a plain ls which is as safe as printf '%s\n' *.
For bugs
shellcheck --versionor "online"): 0.9.0Using a plain
ls | grepand/orls dir/ | grep(with the trailing slash) is safe and predictable. Per POSIX, they would always output one entry per line since the output is piped (i.e. not output to a terminal). Both forms cannot confuse a directory with a file (as inls dir | grep).The relevant bit from POSIX:
Here's a snippet or screenshot that shows the problem:
Here's what shellcheck currently says:
The warning also seems to be misleading. I don't believe
lshas any issues with non-alphanumeric filenames when not outputting to a terminal (only newlines, and many things would break in that case, includingfindwhich is suggested). The warning should be changed to check for arguments not terminated with a slash, or at the very least allow a plainlswhich is as safe asprintf '%s\n' *.Here's what I wanted or expected to see:
No warning.