You only need a minimal change; single-quote the here-document delimiter after <<. cat <<‘EOF’ >> brightup.sh or equivalently backslash-escape it: cat <<\EOF >>brightup.sh Without quoting, the here document will undergo variable substitution, backticks will be evaluated, etc, like you discovered. If you need to expand some, but not all, values, you need to individually escape … Read more
The variable name PATH is already reserved for a different purpose: It lists all the possible locations searched to find commands not built into the shell. ls is such a command. Thus, when you change the value of PATH, you change the way the shell tries to look for the ls executable; unless the new … Read more
From help set : -e Exit immediately if a command exits with a non-zero status. But it’s considered bad practice by some (bash FAQ and irc freenode #bash FAQ authors). It’s recommended to use: trap ‘do_something’ ERR to run do_something function when errors occur. See http://mywiki.wooledge.org/BashFAQ/105
The major one is the ability to nest them, commands within commands, without losing your sanity trying to figure out if some form of escaping will work on the backticks. An example, though somewhat contrived: deps=$(find /dir -name $(ls -1tr 201112[0-9][0-9]*.txt | tail -1l) -print) which will give you a list of all files in … Read more
TL;DR: Since you are using Bash specific features, your script has to run with Bash and not with sh: $ sh myscript.sh myscript.sh: 2: myscript.sh: Bad substitution $ bash myscript.sh ffmpeg -i bar.mp4 bar.mp3 ffmpeg -i foo.mp4 foo.mp3 See Difference between sh and Bash. To find out which sh you are using: readlink -f $(which … Read more
You can copy your crontab into an image, in order for the container launched from said image to run the job. See “Run a cron job with Docker” from Julien Boulay in his Ekito/docker-cron: Let’s create a new file called “hello-cron” to describe our job. # must be ended with a new line “LF” (Unix) … Read more
A Few Introductory Words If at all possible, don’t use shell-quoted strings as an input format. It’s hard to parse consistently: Different shells have different extensions, and different non-shell implementations implement different subsets (see the deltas between shlex and xargs below). It’s hard to programmatically generate. ksh and bash have printf ‘%q’, which will generate … Read more
The backticks/gravemarks have been deprecated in favor of $() for command substitution because $() can easily nest within itself as in $(echo foo$(echo bar)). There are other differences such as how backslashes are parsed in the backtick/gravemark version, etc. See BashFAQ/082 for several reasons to always prefer the $(…) syntax. Also see the POSIX spec … Read more
This is an antipattern because it introduces complexity that wouldn’t exist if you didn’t require the exit status to be recorded at all. if your_command; then … has much less to go wrong than your_command if [ “$?” -eq 0 ]; then … For examples of things that can go wrong: Think about traps, or … Read more
TL;DR: Your script or data has Windows style CRLF line endings. Convert to Unix style by deleting the carriage returns. How do I check if my script or data has carriage returns? They’re detectable as ^M in the output of cat -v yourscript: $ cat -v myscript ls -l myfile^M If your script doesn’t have … Read more