Bash can be pretty obtuse sometimes. The following commands all return different error messages for basically the same error: $ echo hello > bash: syntax error near unexpected token `newline` $ echo hello > ${NONEXISTENT} bash: ${NONEXISTENT}: ambiguous redirect $ echo hello > “${NONEXISTENT}” bash: : No such file or directory Adding quotes around the … Read more
Depending on what you want to do xargs also can help (here: converting documents with pdf2ps): cpus=$( ls -d /sys/devices/system/cpu/cpu[[:digit:]]* | wc -w ) find . -name \*.pdf | xargs –max-args=1 –max-procs=$cpus pdf2ps From the docs: –max-procs=max-procs -P max-procs Run up to max-procs processes at a time; the default is 1. If max-procs is 0, … Read more
Try envsubst FOO=foo BAR=bar export FOO BAR envsubst <<EOF FOO is $FOO BAR is $BAR EOF
Single [] are posix shell compliant condition tests. Double [[]] are an extension to the standard [] and are supported by bash and other shells (e.g. zsh, ksh). They support extra operations (as well as the standard posix operations). For example: || instead of -o and regex matching with =~. A fuller list of differences … Read more
If you know you’re always going to use Bash, it’s much easier to always use the double bracket conditional compound command [[ … ]], instead of the POSIX-compatible single bracket version [ … ]. Inside a [[ … ]] compound, word-splitting and pathname expansion are not applied to words, so you can rely on if … Read more
chmod u+x program_name. Then execute it. If that does not work, copy the program from the USB device to a native volume on the system. Then chmod u+x program_name on the local copy and execute that. Unix and Unix-like systems generally will not execute a program unless it is marked with permission to execute. The … Read more
The following sends standard output to the null device (bit bucket). scriptname >/dev/null And if you also want error messages to be sent there, use one of (the first may not work in all shells): scriptname &>/dev/null scriptname >/dev/null 2>&1 scriptname >/dev/null 2>/dev/null And, if you want to record the messages, but not see them, … Read more
Bash has a handy SECONDS builtin variable that tracks the number of seconds that have passed since the shell was started. This variable retains its properties when assigned to, and the value returned after the assignment is the number of seconds since the assignment plus the assigned value. Thus, you can just set SECONDS to … Read more
This is how I do it. Essentially by using Bash’s backtick command substitution one can place these comments anywhere along a long command line even if it is split across lines. I have put the echo command in front of your example so that you can execute the example and see how it works: echo … Read more
Add this to your crontab (temporarily): * * * * * env > ~/cronenv After it runs, do this: env – `cat ~/cronenv` /bin/sh This assumes that your cron runs /bin/sh, which is the default regardless of the user’s default shell. Footnote: if env contains more advanced config, eg PS1=$(__git_ps1 ” (%s)”)$, it will error … Read more