In Bash, there appear to be several variables which hold special, consistently-meaning values. For instance, ./myprogram &; echo $! will return the PID of the process which backgrounded myprog...
bash - What are the special dollar sign shell variables ... - Stack ...
Here-strings in bash are implemented via temporary files, usually in the format /tmp/sh-thd.bash - What is the purpose of "&&" in a shell command? - Stack Overflow
What is the operator =~ called? I'm not sure it has a name. The bash documentation just calls it the =~ operator. Is it only used to compare the right side against the left side? The right side is considered an extended regular expression. If the left side matches, the operator returns 0, and 1 otherwise. Why are double square brackets required when running a test? Because =~ is an operator of ...
For understanding bash code it is usually very helpful to set the -x option: set -x # within a script / function or when calling a script: bash -vx ./script.sh With loops this is a little less helpful. But you can always take the first part of the command and do this: echo for url in $(cat example.txt) That shows you what happens there (at least the result). This feature is called "command ...
bash - What does $ ( ... ) mean in the shell? - Unix & Linux Stack Exchange
The reason is that Bash is untyped. The -eq causes the strings to be interpreted as integers if possible including base conversion: ... And 0 if Bash thinks it is just a string: ... So [[ "yes" -eq "no" ]] is equivalent to [[ 0 -eq 0 ]] Last note: Many of the Bash specific extensions to the Test Constructs are not POSIX and therefore may fail ...
Furthermore, when you use bash -c, behavior is different than if you run an executable shell script, because in the latter case the argument with index 0 is the shell command used to invoke it.
However in Bash, introducing a pipe means the individual commands are run in subshells. Consider this: ... The output of the 2nd echo command prints just a single space. Whaaaa? What happened to my variables? Because the read command is in a pipeline, it is run in a subshell. It correctly reads 2 words from its stdin and assigns to the variables.
bash - What does <<< mean? - Unix & Linux Stack Exchange
In general, in bash and other shells, you escape special characters using . So, when you use echo foo >> what you are saying is "redirect to a file called > ", but that is because you are escaping the second >. It is equivalent to using echo foo > > which is the same as echo foo > '>'. So, yes, as Sirex said, that is likely a typo in your book.
bash - Difference between >> and - Unix & Linux Stack Exchange
From the manual: (acessible by calling man bash in your shell) ? Expands to the exit status of the most recently executed foreground pipeline. By convention an exit status of 0 means success, and non-zero return status means failure. Learn more about exit statuses on wikipedia.
3 I accidentally replaced my ~/.bash_profile with an empty file. My usually colored screen has turned black and white. (I'm running in command-line-mode with Raspbian Stretch Lite). How do I reset this file?
How to hide secret information with .bash_profile Ask Question Asked 6 years, 1 month ago Modified 6 years, 1 month ago
Have a look at this question which explains the difference between .bashrc and .bash_profile. X11 will look at your .bashrc while a "regular" Terminal will look at .bash_profile So you will need to use .bash_profile in your case.
EDIT: If the new PATH is exported via .bash_profile, the changes are not effective immediately. Try
I know this question has been asked before, but I can't find a fix for my problem, I just can't get my script to run on startup. Here's my script: #!/bin/bash iptables -A INPUT -m state --state NE...
in your case it would probably be xmodmap -e 'keycode 66=Escape'. by the way: if you don't want to type the command every time you login manually, you can insert the line into your .bash_profile and it is executed automatically with your login.
If you set MY_ENV_VAR in your .bash_profile, it will be set if you login as pi but it will not be set if you start a non-interactive shell as in ssh pi@raspberry.local python ./myscript or a subshell as in sudo -u pi bash.
So one work-around for this would be to enable an auto-login for some user and start the app from ~/.bash_profile -- just beware that means it will then start for any and logins from that user, including ssh, so you might want to create a user dedicated to this purpose who only ever logs in automatically in order to run the app.
Run systemctl set-default graphical.target, assuming an up-to-date system with graphical packages installed. On Wheezy, the equivalent was setting default rulevel to 5 in /etc/inittab: id:5:initdefault: Running startx from .bash_profile is wasteful (it will start every time you open a terminal, crash, and then you'll get to the command prompt), and system applets (network manager, volume ...
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