I want to turn off the PC and copy some files before the battery is empty.
#!/bin/bash
LOW=11460
BAT=`/bin/cat /proc/acpi/battery/BAT1/state | /bin/grep remaining | /usr/bin/awk '{print\$3}'`
if ["$BAT" \< "$LOW"]
then
echo "Turning off"
rsync folder/ otherfolder/
shutdown -h now
fi
But its doesn't work!
Your syntax is incorrect. You are unnecessarily escaping parts of your code and your test expression needs spaces surrounding the variables and a numeric comparison when using the [ construct. e.g.:
#!/bin/bash
LOW=11460
BAT=`/bin/cat /proc/acpi/battery/BAT1/state | /bin/grep remaining | /usr/bin/awk '{print $3}'`
if [ "$BAT" -lt "$LOW" ]
then
echo "Turning off"
rsync folder/ otherfolder/
shutdown -h now
fi
Presuming both /bin and /usr/bin are in your path, I would make the following changes:
BAT=`cat /proc/acpi/battery/BAT1/state | grep remaining | awk '{print $3}'`
Consider also using (()) as your test expression. e.g.
if ((BAT < LOW))
Note: spaces surrounding BAT and LOW are not required when using the (()) test construct, and there is no need to dereference your variable with $ inside (()) unless using brace expansion or array syntax. e.g. ((${#array[#]} < something)).
Additionally, since you are calling a script that requires root privileges to call shutdown, you should test for root EUID at the beginning:
if ((EUID != 0)); then
printf "error: script must be run by root, EUID: '%s' can't.\n" $EUID
exit 0
fi
or if you prefer the normal [ test construct:
if [ $EUID -ne 0 ]; then
...
Related
My goal is to write a shell script take the users that I have already filtered out of a file and check whether those users have a certain string, and if they do, label them as major, if not, nonmajor. My trouble is coming from my first if statement, and I'm not sure if grep is the right way to go in an if statement. Here is what I have:
(
while read i
do
username=`echo $i | grep -v 'CMPSC 1513' | grep -P -v '(?!.*CPSMA 2923)CPSMA' | cut -d'|' -f2`
fullname=`echo $i | grep -v 'CMPSC 1513' | grep -P -v '(?!.*CPSMA 2923)CPSMA' | cut -d'|' -f3`
id=`echo $i | grep -v 'CMPSC 1513' | grep -P -v '(?!.*CPSMA 2923)CPSMA' | cut -d'|' -f4`
if [ $username ]
then
if grep -q "|0510"
then
echo $username":(password):(UID):(GID):"$fullname"+"$id":/home/STUDENTS/majors:/bin/bash"
else
echo $username":(password):(UID):(GID):"$fullname"+"$id":/home/STUDENTS/nonmajors:/bin/bash"
fi
fi
done
)<./cs_roster.txt
Just some info, this is contained in a while loop. In the while loop, i determine whether the person listed should even be major or nonmajor, and my if [ $username ] has been tested and does return all the correct users. At this point the while loop is only running once and then stopping.
Just remove the square brackets and pass $i to grep:
if echo $i | grep -q "|0510"
In your code sample, grep does not have anything to work on.
The "binary operator expected" occurs because you are invoking the command [ with the arguments "grep" and "-q" (you are not invoking grep at all), and [ expects a binary operator where you have specified -q. [ is a command, treated no differently that grep or ls or cat. It is better (IMO) to spell it test, and when invoked by the name test it does not require that its last argument be ]. If you want to use grep in an if statement, just do something like:
if echo "$username" | grep -q "|0510"; then ...
(Although I suspect, depending on the context, there are better ways to accomplish your goal.)
The basic syntax of an if statement is if pipeline; then.... In the common case, the pipeline is the simple command test, and at some point in pre-history, the decision was made to provide the name [ for the test command with the added caveat that its final argument must be ]. I believe this was done in an effort to make if statements look more natural, as if the [ is an operator in the language. Just ignore [ and always use test and much confusion will be avoided.
You can use this code as an exercise. Write an awk script for it, or start with something like
while IFS='|' read -r f1 username fullname id otherfields; do
# I don't know which field you want to test. I will rest with id
if [[ $id =~ ^0510 ]]; then
subdir=majors
else
subdir=nonmajors
fi
echo "${username}:(password):(UID):(GID):${fullname}+${id}:/home/STUDENTS/${subdir}:/bin/bash"
done < <( grep -v 'CMPSC 1513' ./cs_roster.txt | grep -P -v '(?!.*CPSMA 2923)CPSMA' )
This is nice for learning some bash syntax, but consider an awk script for avoiding a while-loop.
I am trying to find the number of a particular process in bash using if condition as
if ps auwx | grep -v grep | grep -ic python -le 2; then echo error; else echo no_error; fi
and I am getting output as
grep: python: No such file or directory
no_error
The one-liner seems to break if I use pipe, and no error is thrown if I omit pipe, and it doesn't matter if I use the absolute path to grep either.I cannot get the required result without the pipe. What am I doing wrong here? I can get this done in a script file, by breaking it into variables and then doing comparing it, but I was using this as an exercise to learn bash. Any help is greatly appreciated.
First of all, the syntax of if command is:
if cmd; then
# cmd exited with status 0 (success)
else
# cmd exited with status >0 (fail)
fi
The cmd above is the so-called list - a sequence of pipelines. Each pipeline is a sequence of commands separated with |.
The -le operator is interpreted only by the test command (also known as [, or [[), not by the if command.
So, when you say:
if ps auwx | grep -v grep | grep -ic python -le 2; then ... fi
you actually call grep with arguments:
grep -ic python -le 2
And since -e is used to specify the search pattern, the argument python is interpreted as a filename of the file to search for pattern 2. That's why grep tells you it can't find file named python.
To test the output of a command pipeline in if, you can use the command substitution inside the [[/[/test (as the other answer suggests):
if [[ $(ps auwx | grep -v grep | grep -ic python) -le 2 ]]; then ... fi
or, within (( .. )), with implicit arithmetic comparisons:
if (( $(ps auwx | grep -v grep | grep -ic python) <= 2 )); then ... fi
using a command substitution in a condition
if [[ $(ps ...) -le 2 ]]; then
I was looking at an answer in another thread about which bracket pair to use with if in a bash script. [[ is less surprising and has more features such as pattern matching (=~) whereas [ and test are built-in and POSIX compliant making them portable.
Recently, I was attempting to test the result of a grep command and it was failing with [: too many arguments. I was using [. But, when I switched to [[ it worked. How would I do such a test with [ in order to maintain the portability?
This is the test that failed:
#!/bin/bash
cat > slew_pattern << EOF
g -x"$
EOF
if [ $(grep -E -f slew_pattern /etc/sysconfig/ntpd) ]; then
echo "slew mode"
else
echo "not slew mode"
fi
And the test that succeeded:
#!/bin/bash
cat > slew_pattern << EOF
g -x"$
EOF
if [[ $(grep -E -f slew_pattern /etc/sysconfig/ntpd) ]]; then
echo "slew mode"
else
echo "not slew mode"
fi
if [ $(grep -E -f slew_pattern /etc/sysconfig/ntpd) ]; then
This command will certainly fail for multiple matches. It will throw an error as the grep output is being split on line ending.
Multiple matches of grep are separated by new line and the test command becomes like:
[ match1 match2 match3 ... ]
which doesn't make much of a sense. You will get different error messages as the number of matches returned by grep (i.e the number of arguments for test command [).
For example:
2 matches will give you unary operator expected error
3 matches will give you binary operator expected error and
more than 3 matches will give you too many arguments error or such, in Bash.
You need to quote variables inside [ to prevent word splitting.
On the other hand, the Bash specific [[ prevents word splitting by default. Thus the grep output doesn't get split on new line and remains a single string which is a valid argument for the test command.
So the solution is to look only at the exit status of grep:
if grep -E -f slew_pattern /etc/sysconfig/ntpd; then
Or use quote when capturing output:
if [ "$(grep -E -f slew_pattern /etc/sysconfig/ntpd)" ]; then
Note:
You don't really need to capture the output here, simply looking at the exit status will suffice.
Additionally, you can suppress output of grep command to be printed with -q option and errors with -s option.
I'm trying to get this function for making it easy to parallelize my bash scripts working. The idea is simple; instead of running each command sequentially, I pipe the command I want to run to this function and it does while read line; run the jobs in the bg for me and take care of logistics.... it doesn't work though. I added set -x by where stuff's executed and it looks like I'm getting weird quotes around the stuff I want executed... what should I do?
runParallel () {
while read line
do
while [ "`jobs | wc -l`" -eq 8 ]
do
sleep 2
done
{
set -x
${line}
set +x
} &
done
while [ "`jobs | wc -l`" -gt 0 ]
do
sleep 1
jobs >/dev/null 2>/dev/null
echo sleeping
done
}
for H in `ypcat hosts | grep fmez | grep -v mgmt | cut -d\ -f2 | sort -u`
do
echo 'ping -q -c3 $H 2>/dev/null 1>/dev/null && echo $H - UP || echo $H - DOWN'
done | runParallel
When I run it, I get output like the following:
> ./myscript.sh
+ ping -q -c3 '$H' '2>/dev/null' '1>/dev/null' '&&' echo '$H' - UP '||' echo '$H' - DOWN
Usage: ping [-LRUbdfnqrvVaA] [-c count] [-i interval] [-w deadline]
[-p pattern] [-s packetsize] [-t ttl] [-I interface or address]
[-M mtu discovery hint] [-S sndbuf]
[ -T timestamp option ] [ -Q tos ] [hop1 ...] destination
+ set +x
sleeping
>
The quotes in the set -x output are not the problem, at most they are another result of the problem. The main problem is that ${line} is not the same as eval ${line}.
When a variable is expanded, the resulting words are not treated as shell reserved constructs. And this is expected, it means that eg.
A="some text containing > ; && and other weird stuff"
echo $A
does not shout about invalid syntax but prints the variable value.
But in your function it means that all the words in ${line}, including 2>/dev/null and the like, are passed as arguments to ping, which set -x output nicely shows, and so ping complains.
If you want to execute from variables complicated commandlines with redirections and conditionals, you will have to use eval.
If I'm understanding this correctly, you probably don't want single quotes in your echo command. Single quotes are literal strings, and don't interpret your bash variable $H.
Like many users of GNU Parallel you seem to have written your own parallelizer.
If you have GNU Parallel http://www.gnu.org/software/parallel/ installed you can do this:
cat hosts | parallel -j8 'ping -q -c3 {} 2>/dev/null 1>/dev/null && echo {} - UP || echo {} - DOWN'
You can install GNU Parallel simply by:
wget http://git.savannah.gnu.org/cgit/parallel.git/plain/src/parallel
chmod 755 parallel
cp parallel sem
Watch the intro videos for GNU Parallel to learn more:
https://www.youtube.com/playlist?list=PL284C9FF2488BC6D1
Put your command in an array.
As being quite a newbie in linux, I have the follwing question.
I have list of files (this time resulting from svn status) and i want to create a script to loop them all and replace tabs with 4 spaces.
So I want from
....
D HTML/templates/t_bla.tpl
M HTML/templates/t_list_markt.tpl
M HTML/templates/t_vip.tpl
M HTML/templates/upsell.tpl
M HTML/templates/t_warranty.tpl
M HTML/templates/top.tpl
A + HTML/templates/t_r1.tpl
....
to something like
for i in <files>; expand -t4;do cp $i /tmp/x;expand -t4 /tmp/x > $i;done;
but I dont know how to do that...
You can use this command:
svn st | cut -c8- | xargs ls
This will cut the first 8 characters leaving only a list of file names, without Subversion flags. You can also add grep before cut to filter only some type of changes, like /^M/. xargs will pass the list of files as arguments to a given command (ls in this case).
I would use sed, like so:
for i in files
do
sed -i 's/\t/ /' "$i"
done
That big block in there is four spaces. ;-)
I haven't tested that, but it should work. And I'd back up your files just in case. The -i flag means that it will do the replacements on the files in-place, but if it messes up, you'll want to be able to restore them.
This assumes that $files contains the filenames. However, you can also use Adam's approach at grabbing the filenames, just use the sed command above without the "$i".
Not asking for any votes, but for the record I'll post the combined answer from #Adam Byrtek and #Dan Fego:
svn st | cut -c8- | xargs sed -i 's/\t/ /'
I could not test it with real subversion output, but this should do the job:
svn st | cut -c8- | while read file; do expand -t4 $file > "$file-temp"; mv "$file-temp" "$file"; done
svn st | cut -c8- will generate a list of files without subversion flags. read will then save each entry in the variable $file and expand is used to replace the tabs with four spaces in each file.
Not quite what you're asking, but perhaps you should be looking into commit hooks in subversion?
You could create a hook to block check-ins of any code that contains tabs at the start of a line, or contains tabs at all.
In the repo directory on your subversion server there'll be a directory called hooks. Put something in there which is executable called 'pre-commit' and it'll be run before anything is allowed to be committed. It can return a status to block the commit if you wish.
Here's what I have to stop php files with syntax errors being checked in:
#!/bin/bash
REPOS="$1"
TXN="$2"
PHP="/usr/bin/php"
SVNLOOK=/usr/bin/svnlook
$SVNLOOK log -t "$TXN" "$REPOS" | grep "[a-zA-Z0-9]" > /dev/null
if [ $? -ne 0 ]
then
echo 1>&2
echo "You must enter a comment" 1>&2
exit 1
fi
CHANGED=`$SVNLOOK changed -t "$TXN" "$REPOS" | awk '{print $2}'`
for LINE in $CHANGED
do
FILE=`echo $LINE | egrep \\.php$`
if [ $? == 0 ]
then
MESSAGE=`$SVNLOOK cat -t "$TXN" "$REPOS" "${FILE}" | $PHP -l`
if [ $? -ne 0 ]
then
echo 1>&2
echo "***********************************" 1>&2
echo "PHP error in: ${FILE}:" 1>&2
echo "$MESSAGE" | sed "s| -| $FILE|g" 1>&2
echo "***********************************" 1>&2
exit 1
fi
fi
done