A common mistake in Bash is to write command-line where there's command a reading a file and whose result is redirected to that file. It can be easily avoided because of : 1) warnings "-bash: file.txt: cannot overwrite existing file" 2) options (often "-i") that let the command directly modify the file but I like to have that small function that does the trick by waiting for the first command to end before trying to write into the file. Lots of things could probably done in a better way, if you know one... Show Sample Output

If your script needs to be run in a terminal, this line at the top will stop it running if you absent-mindedly double-click the icon, perhaps intending to edit it. (Of course this won't help with scripts that run in the background.)

Issues & improvements Race conditions: the check for writability then mv is not fully atomic — another process could create/remove/change the target between the test and mv. Permissions and ownership: mv will preserve contents but the resulting file may have the temp file's permissions/ownership (mktemp default). Signal safety: if interrupted (SIGINT, SIGTERM) the temp file may remain. Portability: uses bash-compatible constructs but relies on mktemp and -a (POSIX [ -a ] is obsolete; better to use -e). Better error messages and exit status handling. Allow optional mode to write to stdout when no filename given. Support setting desired file mode (umask or chmod) and preserve atomic replace semantics. Enhanced version Uses safer existence test ([ -e ] not deprecated -a). Installs traps to clean up temp file on exit/signals. Preserves mode of the existing file (if it exists) or allows a chmod option. Attempts a safer atomic replace: write to temp in same directory as target when a filename is supplied (reduces window for cross-filesystem mv failure and preserves atomicity). If no filename given, writes temp contents to stdout. Returns non-zero on failure and prints concise errors to stderr.