Running the command
cd \`echo -n "~"\`
I get the following error:
bash: cd: ~: No such file or directory
What's the problem if 'cd ~' works fine?
The issue is that bash does not do an additional expansion after command substitution. So while cd ~ is expanded the way you want, cd $(echo '~') does not.
There is a keyword called eval that was created for this sort of situation--it forces the command line to be expanded (evaluated) again. If you use eval on that line, it forces the ~ to be expanded into the user directory, even though the normal time for expansion has already passed. (Because the ~ does not exist until the echo command is run, and at that point, it's too late for expansion.)
eval cd `echo -n "~"`
If you do cd ~, the shell expands ~ to your home directory before executing the command. But if you use double quotes ("~"), then this is taken as a literal string and not expanded.
You can see the difference:
$ echo ~
/home/username
$ echo "~"
~
In order to have ~ expanded by the shell, you need to remove the double quotes.
The escaping behaviour of double quotes is described in the Bash manual: http://www.gnu.org/software/bash/manual/html_node/Double-Quotes.html
You will also get the same issue if you simply do cd "~":
$ cd "~"
bash: cd: ~: No such file or directory
cd doesn't understand that ~ is special. It tries, and fails, to find a directory literally called ~.
The reason that cd ~ works is that bash edits the command before running it. bash replaces cd ~ with cd $HOME, and then expands $HOME to get cd /home/YourUsername.
Therefore,
cd `echo -n "~"`
becomes
cd "~"
Related
$ bl 1
$ sh -c 'bl 1'
sh: bl: command not found
The bl script is located in the user's PATH extension (/home/user/.local/bin) but the sh environment does not seem to be aware of it, the bash is. The main /usr/bin/sh executable symlinks to /usr/bin/bash.
Placing a symlink in /usr/local/bin pointing to the local bl script does seem to fix the issue. Expanding the PATH manually $ PATH=/usr/bin:$HOME/.local/bin sh -c 'bl 1' also solves it, something I don't really understand since both the bash and the sh are aware of the PATH.
$ export -p |grep PATH=
declare -x PATH="/usr/local/sbin:/usr/local/bin:/usr/bin:~/.local/bin"
$ sh -c 'export -p |grep PATH'
export PATH="/usr/local/sbin:/usr/local/bin:/usr/bin:~/.local/bin"
"Something's missing and you have to find it" yet it's hard to look if you don't know what is missing.
$ export -p |grep PATH
declare -x PATH="/usr/local/sbin:/usr/local/bin:/usr/bin:~/.local/bin"
Having a literal ~ is wrong. It should have been expanded to /home/user already. The shell will expand ~ when variables are assigned but not when they're expanded.
$ foo=~ && echo $foo # expanded at assignment
/home/user
$ foo='~' && echo $foo # not expanded since the assignment is quoted
~
Find the shell startup script where ~/.local/bin is added to the $PATH and make sure ~ is not quoted.
Wrong:
PATH="$PATH:~/.local/bin"
Right:
PATH=$PATH:~/.local/bin
I have the following simple bash script:
#!/bin/bash -fx
ls *sh
The problem is that bash add a quote to the pattern and I get wrong output.
+ ls '*sh'
ls: cannot access *sh: No such file or directory
How can I change this behavior?
The output of ls *sh from the terminal is:
$ls *sh
a.bash a.sh b.sh
I tried to add quotes according to this post - "Bash variable containing file wildcard"
without success
That because you're disabling pathname expansion with the -f option.
#!/bin/bash -fx
From man:
-f
Disable filename expansion (globbing).
Someone once showed me how to replace the current command (input line) with the output from a substitution.I suspect it is a readline function but can not remember which.The idea is basically that if you type in something like
$ cd `pwd` <READLINE-MACRO such as M-b or C-a>
then the command line will become:
$ cd /home/username/files
and after you run the command the history file will have cd /home/username/files as opposed to 'cd `pwd`'
According to ยง 8.4.8 "Some Miscellaneous [Readline] Commands" of the Bash Reference Manual:
shell-expand-line (M-C-e)
Expand the line as the shell does. This performs alias and history expansion as well as all of the shell word expansions (see Shell Expansions).
So, just type your command:
cd `pwd`
Then hit Alt+Ctrl+e to effect the command-substitution:
cd /home/username/files
Then hit Enter.
I guess you are finding such case: first you run
cd `pwd`
and then when you run:
!cd
it will seach your history cd command and replace `pwd` to /home/username/files
is it?
$0 expands to the name of the shell script.
$ cat ./sample-script
#!/bin/bash
echo $0
$ chmod 700 ./sample-script
$ ./sample-script
./sample-script
If the shell script is invoked via a symbolic link, $0 expands to its name:
$ ln -s ./sample-script symlinked-script
$ ./symlinked-script
./symlinked-script
How could I get the name of an alias? Here `$0' expands again to the filename:
$ alias aliased-script=./sample-script
$ aliased-script
./sample-script
Aliases are pretty dumb, according to the man page
...Aliases are expanded when a command is read, not when it is executed...
so since bash is basically just replacing a string with another string and then executing it, there's no way for the command to know what was expanded in the alias.
I imagine you already know this, but for the record the answer is: you need cooperation by the code implementing the alias.
alternate_name () {
MY_ALIAS_WAS=alternate_name real_name "$#"
}
or, if you really want to use the superseded alias syntax:
alias alternate_name="MY_ALIAS_WAS=alternate_name real_name"
...and then...
$ cat ~/bin/real_name
#!/bin/sh
echo $0, I was $MY_ALIAS_WAS, "$#"
bash does not make this available. This is why symlinks are used to invoke multiplex commands, and not aliases.
I'm pretty new to Bash scripting and am looking to do the following:
The script's pwd is "/a/b/c/directory_name.git/" and I'd like to cd to "../directory_name" where directory_name could be anything. Is there any easy way to do this?
I'm guessing I'd have to put the result of pwd in a variable and erase the last 4 characters.
tmpd=${PWD##*/}
cd ../${tmpd%.*}
or perhaps more simply
cd ${PWD%.*}
Test
$ myPWD="/a/b/c/directory_name.git"
$ tmpd=${myPWD##*/}
$ echo "cd ../${tmpd%.*}"
cd ../directory_name
*Note: $PWD does not include a trailing slash so the ${param##word} expansion will work just fine.
Try:
cd `pwd | sed -e s/\.git$//`
The backticks execute the command inside, and use the output of that command as a command line argument to cd.
To debug pipelines like this, it's useful to use echo:
echo `pwd | sed -e s/\.git$//`
This should work:
cd "${PWD%.*}"
Didn't expect to get so many answers so fast so I had time to come up with my own inelegant solution:
#!/bin/bash
PWD=`pwd`
LEN=${#PWD}
END_POSITION=LEN-4
WORKING_COPY=${PWD:0:END_POSITION}
echo $WORKING_COPY
cd $WORKING_COPY
There's probably one above that's much more elegant :)
That's what basename is for:
cd ../$(basename "$(pwd)" .git)