I came across this line in one of the shell scripts:
[-f $host_something ] && .$host_something
What are the square brackets with the -f switch supposed to do, and what is the point of ANDing it with the same environment variable?
The [ is actually an actual binary. It's an alias for the test(1) command. It will ignore it's last argument which should be ]. Run man test for further information. It's not really shell syntax.
The square bracket is really an alias for the test tool, so you can look at man test to find out how it works. the -f switch is one of many tests that can be run by this tool, and tests if a file exists and is a regular file.
You need some more spaces.
The command
[ -f $host_something ] && . $host_something
stands for
if [ -f $host_something ]; then
source $host_something
fi
or in words:
When the file given in the variable host_something really is a file, then execute the lines in that file without opening a subshell. You do not want a subshell, since all the settings in the subshell get lost as soon as the subshell is finished.
Related
Is it possible to tell the SHELL, e.g. bash, to use a specific (bash)rc file using .SHELLFLAGS?
Below you will see two examples. The first shows what I want to do, and the second illustrates one way of achieving the desired result.
The reason for me asking is that I have a bashrc file (from OpenFOAM) defining a bunch of variables and functions that I want to use in various recipes.
Thank you for your time.
example (not working)
file: bashrc:
export HELLOWORLD="Hello World"
file: Makefile:
SHELL=/bin/bash
.SHELLFLAGS=--rcfile bashrc --
test:
#\
echo "$${HELLOWORLD}"
example (working)
file: bashrc:
export HELLOWORLD="Hello World"
file: Makefile:
.ONESHELL:
SHELL=/bin/bash
test: ; source bashrc
#\
echo "$${HELLOWORLD}"
If you read the bash man page related to the --rcfile option you'll find:
--rcfile file
Execute commands from file instead of the system wide initial‐
ization file /etc/bash.bashrc and the standard personal initial‐
ization file ~/.bashrc if the shell is interactive (see INVOCA‐
TION below).
Note particularly that the shell must be interactive for this to have any effect, but a shell that make invokes is of course not interactive.
Second, if you read the GNU make manual on .SHELLFLAGS you'll see that the default value is -c (or -ec in POSIX mode); the -c option allows the shell to read the script to run from the command line, which is how make invokes the shell. This means when you replace .SHELLFLAGS with your own value, you have to include that.
So with your makefile when make runs the shell it will use this command line:
/bin/bash --rcfile bashrc -- 'echo "${HELLOWORLD}"'
which is clearly not going to work. You need to set .SHELLFLAGS like this:
.SHELLFLAGS = --rcfile bashrc -ic --
The -i option forces an interactive shell, and you need the -c option to tell make to run the first non-option argument as a command.
I used the have the following tmux shortcut function defined in a separate script and aliased, which worked fine but was messy. I decided to move it to my .zshrc where it naturally belongs, and encountered a problem I wasn't able to figure out.
function t () {re='^[0-9]+$'
if [ "$1" == "kill" ]
then
tmux kill-session -t $2
elif [[ "$1" =~ "$re" ]]
then
tmux attach-session -d -t $1
fi}
I source my .zshrc, call the function, and get:
t:1: = not found
I know the function is defined:
╭─bennett#Io [~] using
╰─○ which t
t () {
re='^[0-9]+$'
if [ "$1" == "kill" ]
then
tmux kill-session -t $2
elif [[ "$1" =~ "$re" ]]
then
tmux attach-session -d -t $1
fi
}
I'm assuming this is complaining about the first line of the function. I've tried shifting the first line of the function down several lines, which doesn't change anything except which line the error message refers to. Any clue what's going on? I haven't found anything relating to this specific issue on SO.
The command [ (or test) only supports a single = to check for equality of two strings. Using == will result in a "= not found" error message. (See man 1 test)
zsh has the [ builtin mainly for compatibility reasons. It tries to implement POSIX where possible, with all the quirks this may bring (See the Zsh Manual).
Unless you need a script to be POSIX compliant (e.g. for compatibility with other shells), I would strongly suggest to use conditional expressions, that is [[ ... ]], instead of [ ... ]. It has more features, does not require quotes or other workarounds for possibly empty values and even allows to use arithmetic expressions.
Wrapping the first conditional in a second set of square-brackets seemed to resolve the issue.
More information on single vs double brackets here:
Is [[ ]] preferable over [ ] in bash scripts?
Looking to make my ~ a cleaner place, I would like to move as much user configuration files into $XDG_CONFIG_HOME, which is ~/.config by default. So I would like to store all my zsh user files in $XDG_CONFIG_HOME/zsh/. So far already have this:
% ls $XDG_CONFIG_HOME/zsh/
histfile zsh_cache zshrc
Easy, you just have to fill your ~/.zshrc. Now the trickiest part seems to make zsh read directly $XDG_CONFIG_HOME/zsh/zshrc without sourcing it from ~/.zshrc. How would you proceed?
One may edit /etc/zsh/zshenv to set $XDG_CONFIG_HOME directories and $ZDOTDIR. This require write privilegies on this files though.
So provided that $HOME is defined when zsh read it (I don't know if it's the case), you may add to your /etc/zsh/zshenv:
if [[ -z "$XDG_CONFIG_HOME" ]]
then
export XDG_CONFIG_HOME="$HOME/.config/"
fi
if [[ -d "$XDG_CONFIG_HOME/zsh" ]]
then
export ZDOTDIR="$XDG_CONFIG_HOME/zsh/"
fi
It is good practice to not put a / at the end of any variable holding a certain path.
For example, $XDG_CONFIG_HOME/zsh translates to "$HOME/.config//zsh" and the / repeats because XDG_CONFIG_HOME ends with a /.
So I think your answer should be -
if [[ -z "$XDG_CONFIG_HOME" ]]
then
export XDG_CONFIG_HOME="$HOME/.config"
fi
if [[ -d "$XDG_CONFIG_HOME/zsh" ]]
then
export ZDOTDIR="$XDG_CONFIG_HOME/zsh"
fi
Variation to psychoslave's answer which uses ${HOME}/.zshenv to initiate the environment. No root access needed.
export XDG_CONFIG_HOME=${XDG_CONFIG_HOME:=${HOME}/.config}
export ZDOTDIR=${ZDOTDIR:=${XDG_CONFIG_HOME}/zsh}
source $ZDOTDIR/.zshenv
This was discussed on this thread on the zsh-users mailing list.
You may want to consider saving history in XDG_DATA_HOME. Specifications can be found at XDG Base Directory Specification.
Write a wrapper for zsh that executes zsh after setting the environment variable ZDOTDIR to where you want zsh to look for the config files.
See: http://zsh.sourceforge.net/Intro/intro_3.html
In my .bash_profile I have the following lines:
PATHDIRS="
/usr/local/mysql/bin
/usr/local/share/python
/opt/local/bin
/opt/local/sbin
$HOME/bin"
for dir in $PATHDIRS
do
if [ -d $dir ]; then
export PATH=$PATH:$dir
fi
done
However I tried copying this to my .zshrc, and the $PATH is not being set.
First I put echo statements inside the "if directory exists" function and I found that the if statement was evaluating to false, even for directories that clearly existed.
Then I removed the directory-exists check, and the $PATH was being set incorrectly like this:
/usr/bin:/bin:/usr/sbin:/sbin:
/usr/local/bin
/opt/local/bin
/opt/local/sbin
/Volumes/Xshare/kburke/bin
/usr/local/Cellar/ruby/1.9.2-p290/bin
/Users/kevin/.gem/ruby/1.8/bin
/Users/kevin/bin
None of the programs in the bottom directories were being found or executed.
What am I doing wrong?
Unlike other shells, zsh does not perform word splitting or globbing after variable substitution. Thus $PATHDIRS expands to a single string containing exactly the value of the variable, and not to a list of strings containing each separate whitespace-delimited piece of the value.
Using an array is the best way to express this (not only in zsh, but also in ksh and bash).
pathdirs=(
/usr/local/mysql/bin
…
~/bin
)
for dir in $pathdirs; do
if [ -d $dir ]; then
path+=$dir
fi
done
Since you probably aren't going to refer to pathdirs later, you might as well write it inline:
for dir in \
/usr/local/mysql/bin \
… \
~/bin
; do
if [[ -d $dir ]]; then path+=$dir; fi
done
There's even a shorter way to express this: add all the directories you like to the path array, then select the ones that exist.
path+=/usr/local/mysql/bin
…
path=($^path(N))
The N glob qualifier selects only the matches that exist. Add the -/ to the qualifier list (i.e. (-/N) or (N-/)) if you're worried that one of the elements may be something other than a directory or a symbolic link to one (e.g. a broken symlink). The ^ parameter expansion flag ensures that the glob qualifier applies to each array element separately.
You can also use the N qualifier to add an element only if it exists. Note that you need globbing to happen, so path+=/usr/local/mysql/bin(N) wouldn't work.
path+=(/usr/local/bin/mysql/bin(N-/))
You can put
setopt shwordsplit
in your .zshrc. Then zsh will perform world splitting like all Bourne shells do. That the default appears to be noshwordsplit is a misfeature that causes many a head scratching. I'd be surprised if it wasn't a FAQ. Lets see... yup:
http://zsh.sourceforge.net/FAQ/zshfaq03.html#l18
3.1: Why does $var where var="foo bar" not do what I expect?
Still not sure what the problem was (maybe newlines in $PATHDIRS)? but changing to zsh array syntax fixed it:
PATHDIRS=(
/usr/local/mysql/bin
/usr/local/share/python
/usr/local/scala/scala-2.8.0.final/bin
/opt/local/Library/Frameworks/Python.framework/Versions/2.6/bin
/opt/local/Library/Frameworks/Python.framework/Versions/2.7/bin
/opt/local/etc
/opt/local/bin
/opt/local/sbin
$HOME/.gem/ruby/1.8/bin
$HOME/bin)
and
path=($path $dir)
I'm trying to write a (sh -bourne shell) script that processes lines as they are written to a file. I'm attempting to do this by feeding the output of tail -f into a while read loop. This tactic seems to be proper based on my research in Google as well as this question dealing with a similar issue, but using bash.
From what I've read, it seems that I should be able to break out of the loop when the file being followed ceases to exist. It doesn't. In fact, it seems the only way I can break out of this is to kill the process in another session. tail does seem to be working fine otherwise as testing with this:
touch file
tail -f file | while read line
do
echo $line
done
Data I append to file in another session appears just file from the loop processing written above.
This is on HP-UX version B.11.23.
Thanks for any help/insight you can provide!
If you want to break out, when your file does not exist any more, just do it:
test -f file || break
Placing this in your loop, should break out.
The remaining problem is, how to break the read line, as this is blocking.
This could you do by applying a timeout, like read -t 5 line. Then every 5 second the read returns, and in case the file does not longer exist, the loop will break. Attention: Create your loop that it can handle the case, that the read times out, but the file is still present.
EDIT: Seems that with timeout read returns false, so you could combine the test with the timeout, the result would be:
tail -f test.file | while read -t 3 line || test -f test.file; do
some stuff with $line
done
I don't know about HP-UX tail but GNU tail has the --follow=name option which will follow the file by name (by re-opening the file every few seconds instead of reading from the same file descriptor which will not detect if the file is unlinked) and will exit when the filename used to open the file is unlinked:
tail --follow=name test.txt
Unless you're using GNU tail, there is no way it'll terminate of its own accord when following a file. The -f option is really only meant for interactive monitoring--indeed, I have a book that says that -f "is unlikely to be of use in shell scripts".
But for a solution to the problem, I'm not wholly sure this isn't an over-engineered way to do it, but I figured you could send the tail to a FIFO, then have a function or script that checked the file for existence and killed off the tail if it'd been unlinked.
#!/bin/sh
sentinel ()
{
while true
do
if [ ! -e $1 ]
then
kill $2
rm /tmp/$1
break
fi
done
}
touch $1
mkfifo /tmp/$1
tail -f $1 >/tmp/$1 &
sentinel $1 $! &
cat /tmp/$1 | while read line
do
echo $line
done
Did some naïve testing, and it seems to work okay, and not leave any garbage lying around.
I've never been happy with this answer but I have not found an alternative either:
kill $(ps -o pid,cmd --no-headers --ppid $$ | grep tail | awk '{print $1}')
Get all processes that are children of the current process, look for the tail, print out the first column (tail's pid), and kill it. Sin-freaking-ugly indeed, such is life.
The following approach backgrounds the tail -f file command, echos its process id plus a custom string prefix (here tailpid: ) to the while loop where the line with the custom string prefix triggers another (backgrounded) while loop that every 5 seconds checks if file is still existing. If not, tail -f file gets killed and the subshell containing the backgrounded while loop exits.
# cf. "The Heirloom Bourne Shell",
# http://heirloom.sourceforge.net/sh.html,
# http://sourceforge.net/projects/heirloom/files/heirloom-sh/ and
# http://freecode.com/projects/bournesh
/usr/local/bin/bournesh -c '
touch file
(tail -f file & echo "tailpid: ${!}" ) | while IFS="" read -r line
do
case "$line" in
tailpid:*) while sleep 5; do
#echo hello;
if [ ! -f file ]; then
IFS=" "; set -- ${line}
kill -HUP "$2"
exit
fi
done &
continue ;;
esac
echo "$line"
done
echo exiting ...
'