I can't seem to find the difference between a script run two different ways.
Here's the script (named test.sh):
#! /bin/bash
printf "%b\n" "\u5A"
When the script is sourced:
. test.sh
> Z ## Result I want ##
When the script is run:
./test.sh
> \u5A ## Result I get ##
I want the run script to give the results of the sourced script... what setting do I need to set/change?
You are probably getting different versions of printf; the script you are sourcing from is probably a /bin/sh script, not a Bash script proper?
Shouldn't you be using \x instead of \u? printf "%b\n" "\x5A" works fine in both cases for me.
(Totally different idea here, so I'm posting it as another answer.)
Try running these at the command line:
builtin printf "%b\n" "\u5A"
/usr/bin/env printf "%b\n" "\u5A"
printf is both a shell builtin and an executable, and you may be getting different ones depending on whether you source or run the script. To find out, insert this in the script and run it each way:
type printf
While you're at it, you may as well insert this line too:
echo $SHELL
That will reveal if you're getting different shells, per tripleee.
HAHA!!! I finally traced down the problem! Read ahead if interested (leave the page if not).
These are the only command that will translate \u properly:
. ./test.sh ## Sourcing the script, hash-bang = #! /bin/sh
. ./test.bash ## Sourcing the script, hash-bang = #! /bin/bash
./test ## Running the script with no hash-bang
All of the following produce identical results in that they do NOT translate \u:
./test.sh ## Script is run from an interactive shell but in a non-interactive shell
## test.sh has first line: #! /bin/sh
/bin/sh -c "./test.sh" ## Running the script in a non-interactive sh shell
/bin/sh -lc "./test.sh" ## Running the script in a non-interactive, login sh shell
/bin/sh -c ". ./test.sh" ## Sourcing the file in a non-interactive sh shell
/bin/sh -lc ". ./test.sh" ## Sourcing the file in a non-interactive, login sh shell
## test.bash has first line: #! /bin/bash
/bin/bash -c "./test.bash" ## Running the script in a non-interactive bash shell
/bin/bash -lc "./test.bash" ## Running the script in a non-interactive, login bash shell
/bin/bash -c ". ./test.bash" ## Sourcing the file in a non-interactive bash shell
/bin/bash -lc ". ./test.bash" ## Sourcing the file in a non-interactive, login bash shell
## And from ***tripleee*** (thanks btw):
/bin/sh --norc; . ./test.sh ## Sourcing from an interactive sh shell without the ~/.bashrc file read
/bin/bash --norc; . ./test.bash ## Sourcing from an interactive bash shell without the ~/.bashrc file read
The only way to get proper translation is to run the script without a hash-bang... and I finally figured out why! Without a hash-bang my system chooses the default shell, which btw is NOT /bin/bash... it turns out to be /opt/local/bin/bash... two different versions of bash!
Finally, I removed the OSX /bin/bash [v3.2.48(1)] and replaced it with the MacPorts /opt/local/bin/bash [v4.2.10(2)] and now running the script works! It actually solved about 10-15 other problems I've had (like ${var,,}, read sN1 char, complete -EC "echo ' '", and a host of other commands I have scattered throughout my scripts, ~/.bashrc amd ~/.profile). Honestly, I really should have noticed when my scripts using associative arrays suddenly crapped out on me... how stupid can I get!?
I've been using bash v4 for a looong time now, and my Lion upgrade went and down-graded bash back to v3 (get with the program Apple!)... ugh, I feel so ashamed! Everyone still using bash v3, upgrade!! bash v4 is has many, many beautiful upgrades over version 3. Type bash --version to see what version you are running. One advantage is now bash can translate \uHEX into Unicode!
Try removing the space in the first line, I seem to recall that can cause problems. Offhand I'd guess that because of that space, you're not getting bash, but sh.
Glad you solved it. Still, you might be looking for a portable solution.
Assuming you are always using the same formatting string, we can just discard it, and use something like this;
printf () {
# Discard format string
shift
perl -CSD -le '
print map { s/^\\u//; chr(hex($_)) } #ARGV' "$#"
}
Edit to add: You would simply add this function definition at the beginning of your existing script, overriding the builtin printf. Obviously, if you also use printf for other stuff, this special-purpose replacement isn't good enough.
You could rename the function to uprintf or something, still. It merely translates a sequence of hex codes to the corresponding Unicode characters, discarding any \u prefix.
Related
I want to check if a command exists on my machine (RedHat) inside a perl script.
Im trying to check if compgen -c contains the desired command, but running it from inside a script just gives me an empty output. Other commands work fine.
example.pl:
my $x = `compgen -c`;
print $x;
# empty output
my $y = `ls -a`;
print $y;
# .
# ..
# example.pl
Are there possible solutions for this? Or is there a better way to check for commands on my machine?
First, Perl runs external commands using /bin/sh, which is nowadays a link to a shell that is a default-of-sorts on your system. Much of the time that is bash, but not always; on RedHat it is.
This compgen is a bash builtin. One way to discover that is to run man compgen (in bash) -- and the bash manual pops up. Another way is type as Dave shows.
To use builtins we generally need to run an explicit shell for them, and they have a varied behavior in regards to whether the shell is "interactive" or not.† I can't find a discussion of that in bash documentation for this builtin but experimentation reveals that you need
my #completions = qx(bash -c "compgen -c")
The quotes are needed so to pass a complete command to a shell that will be started.
Note that this way you don't catch any STDERR out of those commands. That will come out on the terminal, and it can get missed that way. Or, you can redirect that stream in the command, by adding 2>&1 (redirect to STDOUT) at the end of it.
This is one of the reasons to use one of a number of good libraries for running and managing external commands instead of the builtin "backticks" (the qx I use above is an operator form of it.)
† This can be facilitated with -i
my #output_lines = qx(bash -i -c "command with arguments")
It's because compgen is a bash built-in command, not an external command. And when you run a command using backticks, you get your system's default shell - which is probably going to be /bin/sh, not bash.
The solution is to explicitly run bash, using the -c command-line option to give it a command to run.
my $x = `bash -c compgen -c`;
From a bash prompt, you can use type to see how a command is implemented.
$ type ssh
ssh is /usr/bin/ssh
$ type compgen
compgen is a shell builtin
How can I definitively determine if the currently running shell is bash or zsh?
(being able to disambiguate between additional shells is a bonus, but only bash & zsh are 100% necessary)
I've seen a few ways to supposedly do this, but they all have problems (see below).
The best I can think of is to run some syntax that will work on one and not the other, and to then check the errors / outputs to see which shell is running. If this is the best solution, what command would be best for this test?
The simplest solution would be if every shell included a read-only parameter of the same name that identified the shell. If this exists, however, I haven't heard of it.
Non-definitive ways to determine the currently running shell:
# default shell, not current shell
basename "${SHELL}"
# current script rather than current shell
basename "${0}"
# BASH_VERSINFO could be defined in any shell, including zsh
if [ -z "${BASH_VERSINFO+x}" ]; then
echo 'zsh'
else
echo 'bash'
fi
# executable could have been renamed; ps isn't a builtin
shell_name="$(ps -o comm= -p $$)"
echo "${shell_name##*[[:cntrl:][:punct:][:space:]]}"
# scripts can be sourced / run by any shell regardless of shebang
# shebang parsing
On $ prompt, run:
echo $0
but you can't use $0 within a script, as $0 will become the script's name itself.
To find the current shell (let's say BASH) if shebang / magic number executable was #!/bin/bash within a script:
#!/bin/bash
echo "Script is: $0 running using $$ PID"
echo "Current shell used within the script is: `readlink /proc/$$/exe`"
script_shell="$(readlink /proc/$$/exe | sed "s/.*\///")"
echo -e "\nSHELL is = ${script_shell}\n"
if [[ "${script_shell}" == "bash" ]]
then
echo -e "\nI'm BASH\n"
fi
Outputs:
Script is: /tmp/2.sh running using 9808 PID
Current shell used within the script is: /usr/bin/bash
SHELL is = bash
I'm BASH
This will work, if shebang was: #!/bin/zsh (as well).
Then, you'll get the output for SHELL:
SHELL is = zsh
While there is no 100% foolproof way to achieve it, it might help to do a
echo $BASH_VERSION
echo $ZSH_VERSION
Both are shell variables (not environment variables), which are set by the respective shell. In the respective other shell, they are empty.
Of course, if someone on purpose creates a variable of this name, or exports such a variable and then creates a subshell of the different kind, i.e.
# We are in bash here
export BASH_VERSION
zsh # the subshell will see BASH_VERSION even though it is zsh
this approach will fail; but I think if someone is really doing such a thing, he wants to sabotage your code on purpose.
This should work for most Linux systems:
cat /proc/$$/comm
Quick and easy.
Working from comments by #ruakh & #oguzismail, I think I have a solution.
\shopt -u lastpipe 2> /dev/null
shell_name='bash'; : | shell_name='zsh'
So suppose I want to run some commands in bash and then say, octave. Is there any way to run the same file with two different commands? In the example below I want the first part to be run by bash and the second to be run by octave
#!/bin/bash
echo helloooo
#!/bin/octave
plot(1,2)
pause()
There is only one shebang possible at first line of a script.
Not sure of what you want to do here, but you can use the script's name to switch the script interpreter at run-time
Exemple myscript.sh
#!/usr/bin/env bash
case "${0##*.}" in
# Switch script's interpreter based on script's name trailing .extension
sh)
echo helloooo
;;
plot | octave | oct)
octave < <(
# Remove the Bash part of this script
# by deleting lines up to what look like an octave shebang,
# and send it to octave
sed '1,/^#!.*[/[:space:]]\+octave$/d' "$0"
)
;;
esac
exit # Bash stuffs ends here
# Octave stuffs starts here with fake octave shebang
#!/usr/bin/env octave
plot(1,2)
pause()
Then create a link to your script:
ln --symbolic --force myscript.sh myscript.oct
Running it as a Bash script:
./myscript.sh
helloooo
Running as an Octave script:
./myscript.oct
...
You could of course just by-pass the bash script altogether and do output in octave itself. It's a neater solution.
#!/usr/bin/octave
disp('hellooo')
plot(1,2)
pause()
Here is the offending part of my script:
read -d '' TEXT <<'EOF'
Some Multiline
text that
I would like
in
a
var
EOF
echo "$TEXT" > ~/some/file.txt
and the error:
read: 175: Illegal option -d
I use this read -d all over the place and it works fine. Not sure why its not happy now. I'm running the script on Ubuntu 10.10
Fixes? Workarounds?
If you run sh and then try that command, you get:
read: 1: Illegal option -d
If you do it while still in bash, it works fine.
I therefore deduce that your script is not running under bash.
Make sure that your script begins with the line:
#!/usr/bin/env bash
(or equivalent) so that the correct shell is running the script.
Alternatively, if you cannot do that (because the script is not a bash one), just be aware that -d is a bash feature and may not be available in other shells. In that case, you will need to find another way.
The -d option to read is a feature unique to bash, not part of the POSIX standard (which only specifies -r and -p options to read). When you run your script with sh on Ubuntu, it's getting run with dash, which is a POSIX shell, and not bash. If you want the script to run under bash then you should run it with bash, or give it a #!/bin/bash shebang. Otherwise, it should be expected to run under any POSIX sh.
In a C program I can write argv[0] and the new name shows up in a ps listing.
How can I do this in bash?
You can do it when running a new program via exec -a <newname>.
Just for the record, even though it does not exactly answer the original poster's question, this is something trivial to do with zsh:
ARGV0=emacs nethack
I've had a chance to go through the source for bash and it does not look like there is any support for writing to argv[0].
I'm assuming you've got a shell script that you wish to execute such that the script process itself has a new argv[0]. For example (I've only tested this in bash, so i'm using that, but this may work elsewhere).
#!/bin/bash
echo "process $$ here, first arg was $1"
ps -p $$
The output will be something like this:
$ ./script arg1
process 70637 here, first arg was arg1
PID TTY TIME CMD
70637 ttys003 0:00.00 /bin/bash ./script arg1
So ps shows the shell, /bin/bash in this case. Now try your interactive shell's exec -a, but in a subshell so you don't blow away the interactive shell:
$ (exec -a MyScript ./script arg1)
process 70936 here, first arg was arg1
PID TTY TIME CMD
70936 ttys008 0:00.00 /bin/bash /path/to/script arg1
Woops, still showing /bin/bash. what happened? The exec -a probably did set argv[0], but then a new instance of bash started because the operating system read #!/bin/bash at the top of your script. Ok, what if we perform the exec'ing inside the script somehow? First, we need some way of detecting whether this is the "first" execution of the script, or the second, execed instance, otherwise the second instance will exec again, and on and on in an infinite loop. Next, we need the executable to not be a file with a #!/bin/bash line at the top, to prevent the OS from changing our desired argv[0]. Here's my attempt:
$ cat ./script
#!/bin/bash
__second_instance="__second_instance_$$"
[[ -z ${!__second_instance} ]] && {
declare -x "__second_instance_$$=true"
exec -a MyScript "$SHELL" "$0" "$#"
}
echo "process $$ here, first arg was $1"
ps -p $$
Thanks to this answer, I first test for the environment variable __second_instance_$$, based on the PID (which does not change through exec) so that it won't collide with other scripts using this technique. If it's empty, I assume this is the first instance, and I export that environment variable, then exec. But, importantly, I do not exec this script, but I exec the shell binary directly, with this script ($0) as an argument, passing along all the other arguments as well ($#). The environment variable is a bit of a hack.
Now the output is this:
$ ./script arg1
process 71143 here, first arg was arg1
PID TTY TIME CMD
71143 ttys008 0:00.01 MyScript ./script arg1
That's almost there. The argv[0] is MyScript like I want, but there's that extra arg ./script in there which is a consequence of executing the shell directly (rather than via the OS's #! processing). Unfortunately, I don't know how to get any better than this.
Update for Bash 5.0
Looks like Bash 5.0 adds support for writing to special variable BASH_ARGV0, so this should become far simpler to accomplish.
(see release announcement)
( exec -a foo bash -c 'echo $0' )
ps and others inspect two things, none of which is argv0: /proc/PID/comm (for the "process name") and /proc/PID/cmdline (for the command-line). Assigning to argv0 will not change what ps shows in the CMD column, but it will change what the process usually sees as its own name (in output messages, for example).
To change the CMD column, write to /proc/PID/comm:
echo -n mynewname >/proc/$$/comm; ps
You cannot write to or modify /proc/PID/cmdline in any way.
Process can set their own "title" by writing to the memory area in which argv & envp are located (note that this is different than setting BASH_ARGV0). This has the side effect of changing /proc/PID/cmdline as well, which is what some daemons do in order to prettify (hide?) their command lines. libbsd's setproctitle() does exactly that, but you cannot do that in Bash without support of external tools.
I will just add that this must be possible at runtime, at least in some environments. Assigning $0 in perl on linux does change what shows up in ps. I do not know how that is implemented, however. If I can find out, i'll update this.
edit:
Based on how perl does it, it is non-trivial. I doubt there is any bask built in way at runtime but don't know for sure. You can see how perl does sets the process name at runtime.
Copy the bash executable to a different name.
You can do this in the script itself...
cp /bin/bash ./new-name
PATH=$PATH:.
exec new-name $0
If you are trying to pretend you are not a shell script you can rename the script itself to something cool or even " " (a single space) so
exec new-name " "
Will execute bash your script and appears in the ps list as just new-name.
OK so calling a script " " is a very bad idea :)
Basically, to change the name
bash script
rename bash and rename the script.
If you are worried, as Mr McDoom. apparently is, about copying a binary to a new name (which is entirely safe) you could also create a symlink
ln -s /bin/bash ./MyFunkyName
./MyFunkyName
This way, the symlink is what appears in the ps list. (again use PATH=$PATH:. if you dont want the ./)