I am creating a Bash script which reads some other environment variables:
echo "Exporting configuration variables..."
while IFS="=" read -r k v; do
key=$k
value=$v
if [[ ${#key} > 0 && ${#value} > 0 ]]; then
export $key=$value
fi
done < $HOME/myfile
and have the variable:
$a=$b/c/d/e
and want to call $a as in:
cp myOtherFile $a
The result for the destination folder for the copy is "$b/c/d/e", and an error is shown:
"$b/c/d/e" : No such file or directory
because it is interpreted literally as a folder path.
Can this path be reinterpreted before being used in the cp command?
You need eval to do this :
$ var=foo
$ x=var
$ eval $x=another_value
$ echo $var
another_value
I recommend you this doc before using eval : http://mywiki.wooledge.org/BashFAQ/048
And a safer approach is to use declare instead of eval:
declare "$x=another_value"
Thanks to chepner 2 for the latest.
It sounds like you want $HOME/myfile to support Bash notations, such as parameter-expansion. I think the best way to do that is to modify $HOME/myfile to be, in essence, a Bash script:
export a=$b/c/d/e
and use the source builtin to run it as part of the current Bash script:
source $HOME/myfile
... commands ...
cp myOtherFile "$a"
... commands ...
try this
cp myOtherFile `echo $a`
Related
I have a bash script that arrives like:
SCRIPT=$(curl .... | parsing...)
echo $SCRIPT > myfile
But when I try to echo it in a file, some parts get evaluated. (Variables are substituted if any are defined, the * character is replaced by all files in the working directory, etc...)
Can I prevent bash from evaluating any content of a variable, while still echoing?
Yes, use double quotes for that. I'll demonstrate:
$ x='*'
$ echo $x
..list of files..
$ echo '$x'
$x
$ echo "$x"
*
How to assign a bash variable to pathX (if exists) or pathY(if exists) for example:
export EDITOR=/usr/bin/nano || /bin/nano
You can use if. If you want to check if the file is executable, use -x
if [ -x /usr/bin/nano ]; then
export EDITOR=/usr/bin/nano
else
export EDITOR=/bin/nano
fi
Or if you want to be able to use it regardless of the type, use -e
if [ -e /usr/bin/nano ]
A simple conditional inside a loop will do:
export EDITOR=
for choice in "/usr/bin/nano" "/bin/nano" ; do
[[ -x "${choice}" ]] && export EDITOR="${choice}" && break
done
echo "Editor selected is '${EDITOR}'" # debug to see what was chosen
This will select the first in the list that exists and is executable, and does not depend on nano actually being in your path (although, to be honest, it probably should be).
export EDITOR=$(whereis -b nano | awk '{ print $2 }')
Run the whereis command to locate the binary for nano and then use the result (parsed through awk) to set the EDITOR variable.
I have a bunch of Bash scripts and they each make use of the following:
BIN_CHATTR="/usr/bin/chattr"
BIN_CHKCONFIG="/sbin/chkconfig";
BIN_WGET="/usr/bin/wget";
BIN_TOUCH="/bin/touch";
BIN_TAR="/bin/tar";
BIN_CHMOD="/bin/chmod";
BIN_CHOWN="/bin/chown";
BIN_ECHO="/bin/echo";
BIN_GUNZIP="/usr/bin/gunzip";
BIN_PATCH="/usr/bin/patch";
BIN_FIND="/usr/bin/find";
BIN_RM="/bin/rm";
BIN_USERDEL="/usr/sbin/userdel";
BIN_GROUPDEL="/usr/sbin/groupdel";
BIN_MOUNT="/bin/mount";
Is there a way I could just wget a Bash script with global settings like that and then include them in the script I want to run?
Yes, you can put all those variables in a file like "settings.sh" and then do this in your scripts:
source settings.sh
You can keep your variables in a shell script and then source that file:
source /path/to/variables.sh
You should actually use . which in bash is the same thing as source but will offer better portability:
. /path/to/variables.sh
Yes you can. Just add your variables and functions to a file, make it executable and "execute" it at the top of any script that needs to access them. Here's an example:
$ pwd
/Users/joe/shell
$ cat lib.sh
#!/bin/bash
BIN_WGET="/usr/bin/wget"
BIN_MOUNT="/bin/mount"
function test() {
echo "This is a test"
}
$ cat script.sh
#!/bin/bash
. /Users/joe/shell/lib.sh
echo "wget=$BIN_WGET"
test
$ ./script.sh
wget=/usr/bin/wget
This is a test
are you looking for the source command?
mylib.sh:
#!/bin/bash
JAIL_ROOT=/www/httpd
is_root(){
[ $(id -u) -eq 0 ] && return $TRUE || return $FALSE
}
test.sh
#!/bin/bash
# Load the mylib.sh using source comamnd
source mylib.sh
echo "JAIL_ROOT is set to $JAIL_ROOT"
# Invoke the is_root() and show message to user
is_root && echo "You are logged in as root." || echo "You are not logged in as root."
btw - use rsync -a to mirror scripts with +x flag.
Let's say I have following command
$> MYENVVAR=myfolder echo $MYENVVAR && MYENVVAR=myfolder ls $MYENVVAR
I mean that MYENVVAR=myfolder repeats
Is it possible to set it once for both "&&" separated commands while keeping the command on one line?
Assuming you actually need it as an environment variable (even though the example code does not really need an environment variable; some shell variables are not environment variables):
(export MYENVVAR=myfolder; echo $MYENVVAR && ls $MYENVVAR)
If you don't need it as an environment variable, then:
(MYENVVAR=myfolder; echo $MYENVVAR && ls $MYENVVAR)
The parentheses create a sub-shell; environment variables (and plain variables) set in the sub-shell do not affect the parent shell. In both commands shown, the variable is set once and then used twice, once by each of the two commands.
Parentheses spawn a new process, where you can set its own variables:
( MYENVVAR=myfolder; echo 1: $MYENVVAR; ); echo 2: $MYENVVAR;
1: myfolder
2:
Wrapping the commands into a string and using eval on them is one way not yet mentioned:
a=abc eval 'echo $a; echo $a'
a=abc eval 'echo $a && echo $a'
Or, if you want to use a general-purpose many-to-many mapping between environment variables and commands, without the need to quote your commands, you can use my trap-based function below:
envMulti()
{
shopt -s extdebug;
PROMPT_COMMAND="$(trap -p DEBUG | tee >(read -n 1 || echo "trap - DEBUG")); $(shopt -p extdebug); PROMPT_COMMAND=$PROMPT_COMMAND";
eval "trap \"\
[[ \\\"\\\$BASH_COMMAND\\\" =~ ^trap ]] \
|| { eval \\\"$# \\\$BASH_COMMAND\\\"; false; }\" DEBUG";
}
Usage:
envMulti a=aaa b=bbb; eval 'echo $a'; eval 'echo $b'
Note: the eval 'echo...'s above have nothing to do with my script; you can never do a=aaa echo $a directly, because the $a gets expanded too early.
Or use it with env if you prefer (it actually prefixes any commands with anything):
echo -e '#!/bin/bash\n\necho $a' > echoScript.sh
chmod +x echoScript.sh
envMulti env a=aaa; ./echoScript.sh; ./echoScript.sh
Note: created a test script just to demonstrate usage with env, which can't accept built-ins like eval as used in the earlier demo.
Oh, and the above were all intended for running your own shell commands by-hand. If you do anything other than that, make sure you know all the cautions about using eval -- i.e. make sure you trust the source of the commands, etc.
Did you consider using export like
export MYENVVAR=myfolder
then type your commands like echo $MYENVVAR (that would work even in sub-shells) etc
I am trying to work out how to make bash (force?) expand variables in a string (which was loaded from a file).
I have a file called "something.txt" with the contents:
hello $FOO world
I then run
export FOO=42
echo $(cat something.txt)
this returns:
hello $FOO world
It didn't expand $FOO even though the variable was set. I can't eval or source the file - as it will try and execute it (it isn't executable as it is - I just want the string with the variables interpolated).
Any ideas?
I stumbled on what I think is THE answer to this question: the envsubst command:
echo "hello \$FOO world" > source.txt
export FOO=42
envsubst < source.txt
This outputs: hello 42 world
If you would like to continue work on the data in a file destination.txt, push this back to a file like this:
envsubst < source.txt > destination.txt
In case it's not already available in your distro, it's in the
GNU package gettext.
#Rockallite
I wrote a little wrapper script to take care of the '$' problem.
(BTW, there is a "feature" of envsubst, explained at
https://unix.stackexchange.com/a/294400/7088
for expanding only some of the variables in the input, but I
agree that escaping the exceptions is much more convenient.)
Here's my script:
#! /bin/bash
## -*-Shell-Script-*-
CmdName=${0##*/}
Usage="usage: $CmdName runs envsubst, but allows '\$' to keep variables from
being expanded.
With option -sl '\$' keeps the back-slash.
Default is to replace '\$' with '$'
"
if [[ $1 = -h ]] ;then echo -e >&2 "$Usage" ; exit 1 ;fi
if [[ $1 = -sl ]] ;then sl='\' ; shift ;fi
sed 's/\\\$/\${EnVsUbDolR}/g' | EnVsUbDolR=$sl\$ envsubst "$#"
Many of the answers using eval and echo kind of work, but break on various things, such as multiple lines, attempting to escaping shell meta-characters, escapes inside the template not intended to be expanded by bash, etc.
I had the same issue, and wrote this shell function, which as far as I can tell, handles everything correctly. This will still strip only trailing newlines from the template, because of bash's command substitution rules, but I've never found that to be an issue as long as everything else remains intact.
apply_shell_expansion() {
declare file="$1"
declare data=$(< "$file")
declare delimiter="__apply_shell_expansion_delimiter__"
declare command="cat <<$delimiter"$'\n'"$data"$'\n'"$delimiter"
eval "$command"
}
For example, you can use it like this with a parameters.cfg which is really a shell script that just sets variables, and a template.txt which is a template that uses those variables:
. parameters.cfg
printf "%s\n" "$(apply_shell_expansion template.txt)" > result.txt
In practice, I use this as a sort of lightweight template system.
you can try
echo $(eval echo $(cat something.txt))
You don't want to print each line, you want to evaluate it so that Bash can perform variable substitutions.
FOO=42
while read; do
eval echo "$REPLY"
done < something.txt
See help eval or the Bash manual for more information.
Another approach (which seems icky, but I am putting it here anyway):
Write the contents of something.txt to a temp file, with an echo statement wrapped around it:
something=$(cat something.txt)
echo "echo \"" > temp.out
echo "$something" >> temp.out
echo "\"" >> temp.out
then source it back in to a variable:
RESULT=$(source temp.out)
and the $RESULT will have it all expanded. But it seems so wrong !
Single line solution that doesn't need temporary file :
RESULT=$(source <(echo "echo \"$(cat something.txt)\""))
#or
RESULT=$(source <(echo "echo \"$(<something.txt)\""))
If you only want the variable references to be expanded (an objective that I had for myself) you could do the below.
contents="$(cat something.txt)"
echo $(eval echo \"$contents\")
(The escaped quotes around $contents is key here)
If something.txt has only one line, a bash method, (a shorter version of Michael Neale's "icky" answer),
using process & command substitution:
FOO=42 . <(echo -e echo $(<something.txt))
Output:
hello 42 world
Note that export isn't needed.
If something.txt has one or more lines, a GNU sed evaluate method:
FOO=42 sed 's/"/\\\"/g;s/.*/echo "&"/e' something.txt
Following solution:
allows replacing of variables which are defined
leaves unchanged variables placeholders which are not defined. This is especially useful during automated deployments.
supports replacement of variables in following formats:
${var_NAME}
$var_NAME
reports which variables are not defined in environment and returns error code for such cases
TARGET_FILE=someFile.txt;
ERR_CNT=0;
for VARNAME in $(grep -P -o -e '\$[\{]?(\w+)*[\}]?' ${TARGET_FILE} | sort -u); do
VAR_VALUE=${!VARNAME};
VARNAME2=$(echo $VARNAME| sed -e 's|^\${||g' -e 's|}$||g' -e 's|^\$||g' );
VAR_VALUE2=${!VARNAME2};
if [ "xxx" = "xxx$VAR_VALUE2" ]; then
echo "$VARNAME is undefined ";
ERR_CNT=$((ERR_CNT+1));
else
echo "replacing $VARNAME with $VAR_VALUE2" ;
sed -i "s|$VARNAME|$VAR_VALUE2|g" ${TARGET_FILE};
fi
done
if [ ${ERR_CNT} -gt 0 ]; then
echo "Found $ERR_CNT undefined environment variables";
exit 1
fi
foo=45
file=something.txt # in a file is written: Hello $foo world!
eval echo $(cat $file)
$ eval echo $(cat something.txt)
hello 42 world
$ bash --version
GNU bash, version 3.2.57(1)-release (x86_64-apple-darwin17)
Copyright (C) 2007 Free Software Foundation, Inc.
envsubst is a great solution (see LenW's answer) if the content you're substituting is of "reasonable" length.
In my case, I needed to substitute in a file's content to replace the variable name. envsubst requires that the content be exported as environment variables and bash has a problem when exporting environment variables that are more than a megabyte or so.
awk solution
Using cuonglm's solution from a different question:
needle="doc1_base64" # The "variable name" in the file. (A $ is not needed.)
needle_file="doc1_base64.txt" # Will be substituted for the needle
haystack=$requestfile1 # File containing the needle
out=$requestfile2
awk "BEGIN{getline l < \"${needle_file}\"}/${needle}/{gsub(\"${needle}\",l)}1" $haystack > $out
This solution works for even large files.
expenv () {
LF=$'\n'
echo "cat <<END_OF_TEXT${LF}$(< "$1")${LF}END_OF_TEXT" | bash
return $?
}
expenv "file name"
The following works: bash -c "echo \"$(cat something.txt)"\"