General rule: quote it if it can either be empty or contain spaces (or any whitespace really) or special characters (wildcards). Not quoting strings with spaces often leads to the shell breaking apart a single argument into many. $? doesn’t need quotes since it’s a numeric value. Whether $URL needs it depends on what you … Read more
To execute a cmd before every command entered, set a trap on DEBUG. Eg. trap date DEBUG To execute that command before emitting a prompt, set PROMPT_COMMAND: PROMPT_COMMAND=date
Interesting question. I tried to use xargs for this and I found a way. Try this: seq 10 | xargs -i –max-procs=4 bash -c “echo start {}; sleep 3; echo done {}” –max-procs=4 will ensure that no more than four subprocesses are running at a time. The output will look like this: start 2 start … Read more
Yes, but don’t do that. Use an array instead. If you still insist on doing it that way… $ foo1=123 $ bar=foo1 $ echo “${!bar}” 123
You need to use single quotes to prevent interpolation happening in your calling shell. $ bash -c ‘echo arg 0: $0, arg 1: $1’ arg1 arg2 arg 0: arg1, arg 1: arg2 Or escape the variables in your double-quoted string. Which to use might depend on exactly what you want to put in your snippet … Read more
You can add one of the Java path to PATH variable using the following command. export PATH=$PATH:/usr/java/jre1.6.0_24/bin/ You can add this line to .bashrc file in your home directory. Adding this to .bashrc will ensure everytime you open bash it will be PATH variable is updated.
Simply don’t put whole commands in variables. You’ll get into a lot of trouble trying to recover quoted arguments. Also: Avoid using all-capitals variable names in scripts. It is an easy way to shoot yourself in the foot. Don’t use backquotes. Use $(…) instead; it nests better. #! /bin/bash if [ $# -ne 2 ] … Read more
No, it is not ok. All commands in a pipeline execute at the same time, and the shell prepares redirections before executing the commands. So, it is likely that the command will overwrite the file before cat reads it. You need sponge(1) from moreutils.
find your/folder -type f -mtime +13 -exec rm {} \;
Try this: Save the script as apt-proxy (without the .sh extension) in some directory, like ~/bin. Add ~/bin to your PATH, typing export PATH=$PATH:~/bin If you need it permanently, add that last line in your ~/.bashrc. If you’re using zsh, then add it to ~/.zshrc instead. Then you can just run apt-proxy with your arguments … Read more