Consider the following code fragment inside a function:
local -r LSBLK_FAILED="Lsblk failed"
for f in $(lsblk -lno MOUNTPOINT "$DEVPATH"); do
sudo umount "$f";
RET=$?
if (( $RET != 0 )); then
echo "Unable to dismount $f - error $UNABLE_DISMOUNT_PARTITION"
return $UNABLE_DISMOUNT_PARTITION
fi
done
if [[ "$f" -eq "$LSBLK_FAILED" ]]; then
echo "Problem running Lsblk"
fi
The problem I have is that I cannot see how to access the return code for the lsblk command. I can detect whether the command failed but I cannot access the actual return code. Can anyone suggest how I might do this?
You can split the call to lsblk into a separate command. Then you can get its exit status from $?.
l=$(lsblk -lno MOUNTPOINT "$DEVPATH")
if (( !$? )); then
for f in $l; do
// etc.
Actually it seems like you can use a conditional with the assignment as well:
if l=$(lsblk...); then
Related
I want to create a utility function for bash to remove duplicate lines. I am using function
function remove_empty_lines() {
if ! command -v awk &> /dev/null
then
echo '[x] ERR: "awk" command not found'
return
fi
if [[ -z "$1" ]]
then
echo "usage: remove_empty_lines <file-name> [--replace]"
echo
echo "Arguments:"
echo -e "\t--replace\t (Optional) If not passed, the result will be redirected to stdout"
return
fi
if [[ ! -f "$1" ]]
then
echo "[x] ERR: \"$1\" file not found"
return
fi
echo $0
local CMD="awk '!seen[$0]++' $1"
if [[ "$2" = '--reload' ]]
then
CMD+=" > $1"
fi
echo $CMD
}
If I am running the main awk command directly, it is working. But when i execute the same $CMD in the function, I am getting this error
$ remove_empty_lines app.js
/bin/bash
awk '!x[/bin/bash]++' app.js
The original code is broken in several ways:
When used with --reload, it would truncate the output file's contents before awk could ever read those contents (see How can I use a file in a command and redirect output to the same file without truncating it?)
It didn't ever actually run the command, and for the reasons described in BashFAQ #50, storing a shell command in a string is inherently buggy (one can work around some of those issues with eval; BashFAQ #48 describes why doing so introduces security bugs).
It wrote error messages (and other "diagnostic content") to stdout instead of stderr; this means that if your function's output was redirected to a file, you could never see its errors -- they'd end up jumbled into the output.
Error cases were handled with a return even in cases where $? would be zero; this means that return itself would return a zero/successful/truthy status, not revealing to the caller that any error had taken place.
Presumably the reason you were storing your output in CMD was to be able to perform a redirection conditionally, but that can be done other ways: Below, we always create a file descriptor out_fd, but point it to either stdout (when called without --reload), or to a temporary file (if called with --reload); if-and-only-if awk succeeds, we then move the temporary file over the output file, thus replacing it as an atomic operation.
remove_empty_lines() {
local out_fd rc=0 tempfile=
command -v awk &>/dev/null || { echo '[x] ERR: "awk" command not found' >&2; return 1; }
if [[ -z "$1" ]]; then
printf '%b\n' >&2 \
'usage: remove_empty_lines <file-name> [--replace]' \
'' \
'Arguments:' \
'\t--replace\t(Optional) If not passed, the result will be redirected to stdout'
return 1
fi
[[ -f "$1" ]] || { echo "[x] ERR: \"$1\" file not found" >&2; return 1; }
if [ "$2" = --reload ]; then
tempfile=$(mktemp -t "$1.XXXXXX") || return
exec {out_fd}>"$tempfile" || { rc=$?; rm -f "$tempfile"; return "$rc"; }
else
exec {out_fd}>&1
fi
awk '!seen[$0]++' <"$1" >&$out_fd || { rc=$?; rm -f "$tempfile"; return "$rc"; }
exec {out_fd}>&- # close our file descriptor
if [[ $tempfile ]]; then
mv -- "$tempfile" "$1" || return
fi
}
First off the output from your function call is not an error but rather the output of two echo commands (echo $0 and echo $CMD).
And as Charles Duffy has pointed out ... at no point is the function actually running the $CMD.
As for the inclusion of /bin/bash in your function's echo output ... the main problem is the reference to $0; by definition $0 is the name of the running process, which in the case of a function is the shell under which the function is being called. Consider the following when run from a bash command prompt:
$ echo $0
-bash
As you can see from your output this generates /bin/bash in your environment. See this and this for more details.
On a related note, the reference to $0 within double quotes causes the $0 to be evaluated, so this:
local CMD="awk '!seen[$0]++' $1"
becomes
local CMD="awk '!seen[/bin/bash]++' app.js"
I'm thinking what you want is something like:
echo $1 # the name of the file to be processed
local CMD="awk '!seen[\$0]++' $1" # escape the '$' in '$0'
becomes
local CMD="awk '!seen[$0]++' app.js"
That should fix the issues shown in your function's output; as for the other issues ... you're getting a good bit of feedback in the various comments ...
I'm new to bash so assume that I don't understand everything in this simple script as I've been putting this together as of today with no prior experience with bash.
I get this error when I run test.sh:
command substitution: line 29: syntax error near unexpected token `$1,'
./f.sh: command substitution: line 29: `index_of($1, $urls))'
FILE: f.sh
#!/bin/bash
urls=( "example.com" "example2.com")
error_exit()
{
echo "$1" 1>&2
exit 1
}
index_of(){
needle=$1
haystack=$2
for i in "${!haystack[#]}"; do
if [[ "${haystack[$i]}" = "${needle}" ]]; then
echo "${i}"
fi
done
echo -1
}
validate_url_param(){
index=-2 #-2 as flag
if [ $# -eq 0 ]; then
error_exit "No url provided. Exiting"
else
index=$(index_of($1, $urls)) #ERROR POINTS TO THIS LINE
if [ $index -eq -1 ]; then
error_exit "Provided url not found in list. Exiting"
fi
fi
echo $index
}
FILE: test.sh
#!/bin/bash
. ./f.sh
index=$(validate_url_param "example.com")
echo $index
echo "${urls[0]}"
I've lost track of all of the tweaks I tried but google is failing me and I'm sure this is some basic stuff so... thanks in advance.
The immediate error, just like the error message tells you, is that shell functions (just like shell scripts) do not require or accept commas between their arguments or parentheses around the argument list. But there are several changes you could make to improve this code.
Here's a refactored version, with inlined comments.
#!/bin/bash
urls=("example.com" "example2.com")
error_exit()
{
# Include script name in error message; echo all parameters
echo "$0: $#" 1>&2
exit 1
}
# A function can't really accept an array. But it's easy to fix:
# make the first argument the needle, and the rest, the haystack.
# Also, mark variables as local
index_of(){
local needle=$1
shift
local i
for ((i=1; i<=$#; ++i)); do
if [[ "${!i}" = "${needle}" ]]; then
echo "${i}"
# Return when you found it
return 0
fi
done
# Don't echo anything on failure; just return false
return 1
}
validate_url_param(){
# global ${urls[#]} is still a bit of a wart
if [ $# -eq 0 ]; then
error_exit "No url provided. Exiting"
else
if ! index_of "$1" "${urls[#]}"; then
error_exit "Provided url not found in list. Exiting"
fi
fi
}
# Just run the function from within the script itself
validate_url_param "example.com"
echo "${urls[0]}"
Notice how the validate_url_param function doesn't capture the output from the function it is calling. index_of simply prints the result to standard output and that's fine, just let that happen and don't intervene. The exit code tells us whether it succeeded or not.
However, reading the URLs into memory is often not useful or necessary. Perhaps you are simply looking for
grep -Fx example.com urls.txt
I have a bash script which is only meant to used be when sourced.
I want to return from it automatically on any error, similar to what set -e does.
However setting set -e doesn't work for me because it will also exit the users shell.
Right now I'm handling returning manually like this command || return 1, for each command.
You can also use command || true or command || return.
If your requirement is something different, please update more precisely.
You can use trap. E.g.:
// foo.sh
function func() {
trap 'if [ $? -ne 0 ]; then echo "Trapped!"; return ; fi' DEBUG
echo 'foo'
find -name "foo" . 2> /dev/null
echo 'bar'
}
func
Two notes. First, the trap needs to be inside the function as shown. It won't work if it's just inside the script.
Two, there is a significant limitation. Even if you set the return to the trap (e.g., return 1), while func exists after the bad find command, $? is still zero, no matter what. I'm not sure if there's a way around that, so if it's important to preserve the exit value of the failed command, this may not work.
E.g., if you had:
func
func_return=$?
echo "return value is: $func_return"
func_return will always be zero. I've played around with trying to get the exit value of the failed command to pass out of the function trap and into the function exit value, but have not found a way to do it.
If you need to preserve the return value, you could update a global variable inside the debug trap.
If I understand well, you can set -e locally in each function.
cat sourced
f1 () {
local -
set -e
[ "$1" -eq "$1" ] 2> /dev/null && echo "$1"
}
cat script.sh
. sourced
param='bad'
ret=$(f1 "$param")
[ $? -eq 0 ] && echo "result = $ret" || \
echo "error in sourced file with param $param"
param=3
ret=$(f1 "$param")
[ $? -eq 0 ] && echo "result = $ret" || \
echo "error in sourced file with param $param"
I'm currently creating monstrosities like the following:
ll /home && echo -e "==============\n" && getent passwd && echo -e "==============\n" && ll /opt/tomcat/ && echo -e "==============\n" && ll /etc/sudoers.d/
Is there perhaps some program that handles this in a nicer way?
Something like this (the hypothetical name of the program would be multiprint in my example):
multiprint --delim-escapechars true --delim "============\n" '{ll /home},{getent passwd},...'
alternatively:
multiprint -de "============\n" '{ll /home},{getent passwd},...'
A function like the following would give you that ability :
function intersect() {
delim=$1
shift
for f; do cat "$f"; echo "$delim"; done
}
You could call it as follows to implement your specific use-case :
intersect '==============' <(ll /home) <(getent passwd) <(ll /opt/tomcat/) <(ll /etc/sudoers.d/)
You can try it here.
printf will repeat its format until its arguments are exhausted. You could write something like
printf '%s\n================\n' "$(ll /home)" "$(getent passed)" "$(ll /opt/tomcat)" "$(ll /etc/sudoers.d)"
although this is a little memory-intensive, since it buffers all the output in memory until all the commands have completed.
Based on #Aaron's answer I ended up creating this multiprint.sh Bash shell script, and for what it's worth posting it here:
#!/bin/bash
# Print output of multiple commands, delimited by a specified string
function multiprint() {
if [[ -z "$*" ]]; then
__multiprint_usage
return 0
elif [[ "$1" == "--help" ]]; then
__multiprint_usage
return 0
else
delim=$1
shift
for f; do cat "$f"; echo -e "$delim"; done
fi
}
function __multiprint_usage() {
echo "Usage:"
echo " multiprint '<delimiter>' <(cmd1) <(cmd2) ..."
# example: multiprint '\n\n\n' <(ll /home/) <(ll /var/) ..."
}
I am trying to do the following in bash:
get my external IP
read first line of a file
compare both values
if it is not the same, delete the file and recreate it with the current address
I really don't know why this fails, all my script does is to output my current address and the first line of the file (which by the way is simply "asd" for testing)
#!/bin/bash
IP= curl http://ipecho.net/plain
OLD= head -n 1 /Users/emse/Downloads/IP/IP.txt
if [ "$IP" = "$OLD" ]; then
exit
else
rm /Users/emse/Downloads/IP/IP.txt
$IP> /Users/emse/Downloads/IP/IP.txt
exit
fi
Some obvious problems in your script:
Don't put spaces on either side of equal sign if you want to do assignment
You want the output of curl, head so wrap them in backticks (`)
You want to write $IP into the file, not to execute the content of it as a command, so echo it
The script becomes:
#!/bin/bash
IP=`curl http://ipecho.net/plain`
OLD=`head -n 1 /Users/emse/Downloads/IP/IP.txt`
if [ "$IP" = "$OLD" ]; then
exit
else
rm /Users/emse/Downloads/IP/IP.txt
echo $IP > /Users/emse/Downloads/IP/IP.txt
exit
fi
Excellent answer qingbo, just a tad bit of refinement:
#!/bin/bash
IP=`curl http://ipecho.net/plain`
OLD=`head -n 1 /Users/emse/Downloads/IP/IP.txt`
if [ "$IP" != "$OLD" ]; then
echo $IP > /Users/emse/Downloads/IP/IP.txt # > creates/truncates/replaces IP.txt
fi