After I have been following down a challenging problem with my friends, I had an idea to make a blind command substitution.
This one with single quotes,
pid='1024 --help `touch /tmp/helw`' piduser=$(ps -ouser -p$pid h)
does not create the file /tmp/helw
But this one with double quotes,
pid="1024 --help `touch /tmp/helw`" piduser=$(ps -ouser -p$pid h)
creates the file.
My problem is, how can i make command substitution without let it run in pid - variable, but in piduser variable.
First, don't. Separate actions can and should be separate actions.
touch /tmp/helw && ...
...but if for some odd reason this is actually necessary (I can't imagine why), anything done inside $(...) is a subshell and can be several commands.
pid='1024 --help ' piduser=$( touch /tmp/helw && ps -ouser -p$pid h )
Related
My python script can take a series of bitwise operators as one of its arguments. They all work fine except for "=<<" which is roll left, and "=>>" which is roll right. I run my script like ./script.py -b +4,-4,=>>10,=<<1, where anything after -b can be any combination of similar operations. As soon as the terminal sees "<<" though, it just drops the cursor to a new line after the command and asks for more input instead of running the script. When it sees ">>", my script doesn't process the arguments correctly. I know it's because bash uses these characters for a specific purpose, but I'd like to get around it while still using "=>>" and "=<<" in my arguments for my script. Is there any way to do it without enclosing the argument in quotation marks?
Thank you for your help.
You should enclose the parameters that contain special symbols into single quotation marks (here, echo represents your script):
> echo '+4,-4,=>>10,=<<1'
+4,-4,=>>10,=<<1
Alternatively, save the parameters to a file (say, params.txt) and read them from the file onto the command line using the backticks:
> echo `cat params.txt`
+4,-4,=>>10,=<<1
Lastly, you can escape some offending symbols:
> echo +4,-4,=\>\>10,=\<\<1
+4,-4,=>>10,=<<1
I have a BASH script that has a long set of arguments and two ways of calling it:
my_script --option1 value --option2 value ... etc
or
my_script val1 val2 val3 ..... valn
This script in turn compiles and runs a large FORTRAN code suite that eventually produces a netcdf file as output. I already have all the metadata in the netcdf output global attributes, but it would be really nice to also include the full run command one used to create that experiment. Thus another user who receives the netcdf file could simply reenter the run command to rerun the experiment, without having to piece together all the options.
So that is a long way of saying, in my BASH script, how do I get the last command entered from the parent shell and put it in a variable? i.e. the script is asking "how was I called?"
I could try to piece it together from the option list, but the very long option list and two interface methods would make this long and arduous, and I am sure there is a simple way.
I found this helpful page:
BASH: echoing the last command run
but this only seems to work to get the last command executed within the script itself. The asker also refers to use of history, but the answers seem to imply that the history will only contain the command after the programme has completed.
Many thanks if any of you have any idea.
You can try the following:
myInvocation="$(printf %q "$BASH_SOURCE")$((($#)) && printf ' %q' "$#")"
$BASH_SOURCE refers to the running script (as invoked), and $# is the array of arguments; (($#)) && ensures that the following printf command is only executed if at least 1 argument was passed; printf %q is explained below.
While this won't always be a verbatim copy of your command line, it'll be equivalent - the string you get is reusable as a shell command.
chepner points out in a comment that this approach will only capture what the original arguments were ultimately expanded to:
For instance, if the original command was my_script $USER "$(date +%s)", $myInvocation will not reflect these arguments as-is, but will rather contain what the shell expanded them to; e.g., my_script jdoe 1460644812
chepner also points that out that getting the actual raw command line as received by the parent process will be (next to) impossible. Do tell me if you know of a way.
However, if you're prepared to ask users to do extra work when invoking your script or you can get them to invoke your script through an alias you define - which is obviously tricky - there is a solution; see bottom.
Note that use of printf %q is crucial to preserving the boundaries between arguments - if your original arguments had embedded spaces, something like $0 $* would result in a different command.
printf %q also protects against other shell metacharacters (e.g., |) embedded in arguments.
printf %q quotes the given argument for reuse as a single argument in a shell command, applying the necessary quoting; e.g.:
$ printf %q 'a |b'
a\ \|b
a\ \|b is equivalent to single-quoted string 'a |b' from the shell's perspective, but this example shows how the resulting representation is not necessarily the same as the input representation.
Incidentally, ksh and zsh also support printf %q, and ksh actually outputs 'a |b' in this case.
If you're prepared to modify how your script is invoked, you can pass $BASH_COMMANDas an extra argument: $BASH_COMMAND contains the raw[1]
command line of the currently executing command.
For simplicity of processing inside the script, pass it as the first argument (note that the double quotes are required to preserve the value as a single argument):
my_script "$BASH_COMMAND" --option1 value --option2
Inside your script:
# The *first* argument is what "$BASH_COMMAND" expanded to,
# i.e., the entire (alias-expanded) command line.
myInvocation=$1 # Save the command line in a variable...
shift # ... and remove it from "$#".
# Now process "$#", as you normally would.
Unfortunately, there are only two options when it comes to ensuring that your script is invoked this way, and they're both suboptimal:
The end user has to invoke the script this way - which is obviously tricky and fragile (you could however, check in your script whether the first argument contains the script name and error out, if not).
Alternatively, provide an alias that wraps the passing of $BASH_COMMAND as follows:
alias my_script='/path/to/my_script "$BASH_COMMAND"'
The tricky part is that this alias must be defined in all end users' shell initialization files to ensure that it's available.
Also, inside your script, you'd have to do extra work to re-transform the alias-expanded version of the command line into its aliased form:
# The *first* argument is what "$BASH_COMMAND" expanded to,
# i.e., the entire (alias-expanded) command line.
# Here we also re-transform the alias-expanded command line to
# its original aliased form, by replacing everything up to and including
# "$BASH_COMMMAND" with the alias name.
myInvocation=$(sed 's/^.* "\$BASH_COMMAND"/my_script/' <<<"$1")
shift # Remove the first argument from "$#".
# Now process "$#", as you normally would.
Sadly, wrapping the invocation via a script or function is not an option, because the $BASH_COMMAND truly only ever reports the current command's command line, which in the case of a script or function wrapper would be the line inside that wrapper.
[1] The only thing that gets expanded are aliases, so if you invoked your script via an alias, you'll still see the underlying script in $BASH_COMMAND, but that's generally desirable, given that aliases are user-specific.
All other arguments and even input/output redirections, including process substitutiions <(...) are reflected as-is.
"$0" contains the script's name, "$#" contains the parameters.
Do you mean something like echo $0 $*?
I wrote hook for command line:
# Transforms command 'ls?' to 'man ls'
function question_to_man() {
if [[ $2 =~ '^\w+\?$' ]]; then
man ${2[0,-2]}
fi
}
autoload -Uz add-zsh-hook
add-zsh-hook preexec question_to_man
But when I do:
> ls?
After exiting from man I get:
> zsh: no matches found: ls?
How can I get rid of from message about wrong command?
? is special to zsh and is the wildcard for a single character. That means that if you type ls? zsh tries find matching file names in the current directory (any three letter name starting with "ls").
There are two ways to work around that:
You can make "?" "unspecial" by quoting it: ls\?, 'ls?' or "ls?".
You make zsh handle the cases where it does not match better:
The default behaviour if no match can be found is to print an error. This can be changed by disabling the NOMATCH option (also NULL_GLOB must not be set):
setopt NO_NOMATCH
setopt NO_NULL_GLOB
This will leave the word untouched, if there is no matching file.
Caution: In the (maybe unlikely) case that there is a file with a matching name, zsh will try to execute a command with the name of the first matching file. That is if there is a file named "lsx", then ls? will be replaced by lsx and zsh will try to run it. This may or may not fail, but will most likely not be the desired effect.
Both methods have their pro and cons. 1. is probably not exactly what you are looking for and 2. does not work every time as well as changes your shells behaviour.
Also (as #chepner noted in his comment) preexec runs additionally to not instead of a command. That means you may get the help for ls but zsh will still try to run ls? or even lsx (or another matching name).
To avoid that, I would suggest defining a command_not_found_handler function instead of preexec. From the zsh manual:
If no external command is found but a function command_not_found_handler exists the shell executes this function with all command line arguments. The function should return status zero if it successfully handled the command, or non-zero status if it failed. In the latter case the standard handling is applied: ‘command not found’ is printed to standard error and the shell exits with status 127. Note that the handler is executed in a subshell forked to execute an external command, hence changes to directories, shell parameters, etc. have no effect on the main shell.
So this should do the trick:
command_not_found_handler () {
if [[ $1 =~ '\?$' ]]; then
man ${1%\?}
return 0
else
return 1
fi
}
If you have a lot of matching file names but seldomly misstype commands (the usual reason for "Command not found" errors) you might want to consider using this instead:
command_not_found_handler () {
man ${1%?}
}
This does not check for "?" at the end, but just cuts away any last character (note the missing "\" in ${1%?}) and tries to run man on the rest. So even if a file name matches, man will be run unless there is indeed a command with the same name as the matched file.
Note: This will interfere with other tools using command_not_found_handler for example the command-not-found tool from Ubuntu (if enabled for zsh).
That all being said, zsh has a widget called run-help which can be bound to a key (in Emacs mode it is by default bound to Alt+H) and than runs man for the current command.
The main advantages of using run-help over the above are:
You can call it any time while typing a longer command, as long as the command name is complete.
After you leave the manpage, the command is still there unchanged, so you can continue writing on it.
You can even bind it to Alt+? to make it more similar: bindkey '^[?' run-help
I'am new in Linux and I want to write a bash script that can read in a file name of a directory that starts with LED + some numbers.(Ex.: LED5.5.002)
In that directory there is only one file that will starts with LED. The problem is that this file will every time be updated, so the next time it will be for example LED6.5.012 and counting.
I searched and tried a little bit and came to this solution:
export fspec=/home/led/LED*
LedV=`basename $fspec`
echo $LedV
If I give in those commands one by one in my terminal it works fine, LedV= LED5.5.002 but if i run it in a bash scripts it gives the result: LedV = LED*
I search after another solution:
a=/home/led/LED*
LedV=$(basename $a)
echo $LedV
but here again the same, if i give it in one by one it's ok but in a script: LedV = LED*.
It's probably something small but because of my lack of knowledge over Linux I cannot find it. So can someone tell what is wrong?
Thanks! Jan
Shell expansions don't happen on scalar assignments, so in
varname=foo*
the expansion of "$varname" will literally be "foo*". It's more confusing when you consider that echo $varname (or in your case basename $varname; either way without the double quotes) will cause the expansion itself to be treated as a glob, so you may well think the variable contains all those filenames.
Array expansions are another story. You might just want
fspec=( /path/LED* )
echo "${fspec[0]##*/}" # A parameter expansion to strip off the dirname
That will work fine for bash. Since POSIX sh doesn't have arrays like this, I like to give an alternative approach:
for fspec in /path/LED*; do
break
done
echo "${fspec##*/}"
pwd
/usr/local/src
ls -1 /usr/local/src/mysql*
/usr/local/src/mysql-cluster-gpl-7.3.4-linux-glibc2.5-x86_64.tar.gz
/usr/local/src/mysql-dump_test_all_dbs.sql
if you only have 1 file, you will only get 1 result
MyFile=`ls -1 /home/led/LED*`
When I'm programming, I'll find myself cycling through the same three shell commands, e.g:
vim myGraphic.cpp
g++ -lglut -lGLU myGraphic.cpp -o prettyPicture
./prettyPicture
In order to avoid hitting the uparrow key thrice every time, I put the following in my bashrc:
function cyc {
CYCLE=3
!-$CYCLE
}
When I use the 'cyc' function, however, I get the error
"bash: !-3: command not found".
This technique of history expansion works interactively with the shell, but it does not seem to work with function definitions. What is the explanation for this difference? How might I make a function equivalent to 'cyc' that works?
This question has been asked here: use "!" to execute commands with same parameter in a script but in brief you need to
set -o history
set -o histexpand
in your script to enable history expansion.
History expansion seems to be expanded immediately, whereas other commands inside the body of a function are deferred until the function is called. Try defining the function at a shell prompt. I get bash: !-$CYCLE: event not found immediately, before the function definition is complete.
I tried escaping the exclamation point, but this causes it to be treated literally once the function is called, instead of being processed as a history expansion.
One alternative is a combination of eval and fc:
function cyc {
CYCLE=3
eval $( fc -nl -$CYCLE -$CYCLE )
}
I'll forgo the usual warning about eval because you'll simply be re-executing a command you previously ran, so caution will apply however you accomplish this. The given fc command will print a range of commands from history (-n suppresses the line number), and using the same value for the beginning and end of the range limits the output to a single command.
One way. It extract last four lines of your history, taking into account that history will be included, from that extract the first one for same result that !-3 and use perl to remove either the history number and leading spaces before executing the instruction.
function cyc {
CYCLE=4
history | tail -"$CYCLE" | head -1 | perl -ne 's/\A\s*\d+\s*// && system( $_ )'
}