Strings are typically delimited by quotes, which raises the problem of dealing with strings that include quotes.
27
votes
7answers
3k views
How do I delete a file whose name begins with “-” (hyphen a.k.a. dash or minus)?
How do you remove a file whose filename begins with a dash (hyphen or minus) -? I'm ssh'd into a remote OSX server and I have this file in my directory:
tohru:~ $ ls -l
total 8
-rw-r--r-- 1 me ...
24
votes
2answers
2k views
$VAR vs ${VAR} and to quote or not to quote
I can write
VAR=$VAR1
VAR=${VAR1}
VAR="$VAR1"
VAR="${VAR1}"
the end result to me all seems about the same. Why should I write one or the other? are any of these not portable/POSIX?
20
votes
2answers
660 views
Why escape trivial characters in shell script?
I just opened a legacy shell script (written in old ksh88 on Solaris) and found the following repeated all throughout the code:
[ -f $myfile ] && \rm -f $myfile
The escaping backslash ...
19
votes
3answers
2k views
using single or double bracket - bash
I'm confused with using single or double bracket. look at code:
dir="/home/mazimi/VirtualBox VMs"
if [[ -d ${dir} ]]; then
echo "yep"
fi
It works perfectly although the string contains space. ...
18
votes
1answer
652 views
Why doesn't 'find' show this file?
Using find with grep, one can locate files that match a pattern:
# find | grep error
./solr-modifiedSolr4/SolrPhpClient/phpdocs/errors.html
./error_log
./includes/classes/error_log
However, using ...
17
votes
3answers
5k views
Quoting in ssh $host $FOO and ssh $host “sudo su user -c $FOO” type constructs
I often end up issuing complex commands over ssh; these commands involve piping to awk or perl one-lines, and as a result contain single quotes and $'s. I have neither been able to figure out a hard ...
13
votes
5answers
4k views
How to add newlines into variables in bash script
When I do
str="Hello World\n===========\n"
I get the \n printed out too. How can I have newlines then?
12
votes
3answers
2k views
Can't use exclamation mark (!) in bash?
I'm trying to use the curl command to access a http url with a exclamation mark (!) in its path. e.g:
curl -v "http://example.org/!287s87asdjh2/somepath/someresource"
the console replies with bash: ...
11
votes
3answers
1k views
What does it mean to have a $“dollarsign-prefixed string” in a script?
I just saw this in an init script:
echo $"Stopping Apache"
What is that dollar-sign for?
My research so far:
I found this in the bash manual:
extquote
If set, $'string' and ...
11
votes
2answers
503 views
gnu find and masking the {} for some shells - which?
The man page for gnu find states:
-exec command ;
[...] The string `{}' is replaced by the current
file name being processed everywhere it occurs in the
arguments to the command, ...
9
votes
5answers
359 views
Why do I need to quote variable for if, but not for echo?
I've read that you need double quotes for expanding variables, e.g.
if [ -n "$test" ]; then echo '$test ok'; else echo '$test null'; fi
will work as expected, while
if [ -n $test ]; then echo ...
8
votes
2answers
1k views
What is the significance of single and double quotes in environment variables?
I defined some environment variables in my .profile like this:
MY_HOME="/home/my_user"
but the variable does not seem to evaluate unless I strip off the quotes and re-source the file. I believe ...
8
votes
1answer
1k views
How can I execute `date` inside of a cron tab job?
I want to create a log file for a cron script that has the current hour in the log file name. This is the command I tried to use:
0 * * * * echo hello >> ~/cron-logs/hourly/test`date "+%d"`.log
...
8
votes
2answers
1k views
How are parenthesis interpreted at the command line?
While reading up on how to set up grub, one article mentioned that I need to use a syntax like
echo \(hd0,0\) >> /boot/grub/grub.conf
or
echo '(hd0,0)' >> /boot/grub/grub.conf
...
7
votes
2answers
143 views
When is double-quoting necessary?
The old advice used to be to double-quote any expression involving a $VARIABLE, at least if one wanted it to be interpreted by the shell as one single item, otherwise, any spaces in the content of ...
7
votes
3answers
6k views
What does ` (backquote/backtick) mean in bash?
I came across the following command
sudo chown `id -u` /somedir
And I wonder what is the meaning of the ` symbol. I noticed for instance that while the command above works well the one below does ...
6
votes
2answers
261 views
Why does --text=“$@” only pass the first word?
When I run the following script with some arguments like arg1 arg2 arg3:
#!/bin/bash
zenity --entry --text="$@"
zenity creates an entry dialog with this text: "arg1" whereas I expect "arg1 arg2 ...
6
votes
3answers
8k views
What characters do I need to escape when using sed in a sh script?
Take the following script:
#!/bin/sh
sed 's/(127\.0\.1\.1)\s/\1/' [some file]
If I try to run this in sh (dash here), it'll fail because of the parentheses, which need to be escaped. But I don't ...
6
votes
1answer
135 views
Wildcards inside quotes
This will be an easy one, but in my memories, when shell scripting, using double quotes would allow expanding globbing and variables.
But in the following code:
#!/bin/sh
echo *.sh
echo "*.sh"
echo ...
6
votes
2answers
2k views
How to properly escape exclamation points in bash?
Today, I was caught redhanded while attempting to code golf a password generator for Twitter.
import string as s,random;print ''.join(random.sample(s.letters+s.digits+s.punctuation,9))
90 chars. ...
5
votes
3answers
869 views
How to wget Youtube horrible URL
I'm going to wget youtube search page where the URL is horrible. This is example when searching searchkeyword sorted by upload date:
wget ...
5
votes
2answers
112 views
Bash : command line with optional arguments
I'm running this kind of code:
#!/usr/bin/env bash
set -u
exclude1='--exclude=/path/*'
exclude2='--exclude=/path with spaces/*'
exclude3='' # any 'exclude' can be empty
tar -czf backup.tgz ...
5
votes
2answers
275 views
Bash, curious about echo $variable
I was hacking at a small script earlier and noticed something I can't explain.
Running this command
(time wget --spider http://www.google.co.uk/) 2>&1 | egrep 'real|response'
gives me ...
5
votes
1answer
1k views
Dollar sign interpolation inside quotes in bash
I am running this little test script I wrote :
#!/bin/bash
TESTCASE=$@
testHarness <<runTest
$TESTCASE
runTest
from the command line :
./test.sh "1092$212"
but the dollar sign is being ...
5
votes
2answers
666 views
Number of backslashes needed for escaping regex backslash on the command-line
I recently had trouble with some regex on the command-line, and
found that for matching a backslash, different numbers of
characters can be used. This number depends on the quoting used for
the regex ...
5
votes
1answer
2k views
Remote for-loop over SSH
I have the following in a script
for server in ${servers[@]}; do
echo ${server}
ssh user@${server} "for i in /tmp/foo* ; do echo ${i}; done"
done
But it doesn't work. Weird thing, I see $I amount ...
4
votes
5answers
675 views
How to enclose in quotes if both single and double quotes are already used?
I don't remember the exact commands and tricks that I use sometimes which solves much of the work, so I try to log them into a file for future reference. What I typically do is just put whole command ...
4
votes
5answers
123 views
How to use ' in alias?
I have one-line that I want to call using alias.
while printf '%s ' "$(df -P / | awk 'NR==2 { print $(NF-1) }')"; do sleep 30; done
I tried to escape ' like \' but it didn't work.
What is the ...
4
votes
2answers
193 views
Understanding quotes in a bash conditional instruction
My friend is messing around with Bash scripts and he wanted me to take a look at them (he had another friend do it for him). One of the commands is
if [ "`pidof transmmission-gtk`"=0 ];
what ...
4
votes
1answer
124 views
find usage - command line vs script
I am seeing different results from the find command between being run manually on the command line vs run in a script.
If I run the following on the command line:
find . -name '*.txt' ! -name ...
4
votes
2answers
2k views
Why does the exclamation mark `!` sometimes upset bash?
I realize that ! has special significance on the commandline in the context of the commandline history, but aside from that, in a runing script the exclamation mark can sometimes cause a parsing ...
4
votes
3answers
2k views
Why the double quotes and backquotes in a shell script?
I'm looking at this script mysql backup script and I don't understand what is the reason for using both backticks and double quotes around command names?
379 WHICH="`which which`"
380 AWK="`${WHICH} ...
4
votes
2answers
198 views
Bash prompt not recognizing Unicode escapes
I'm trying to customize my Bash prompt with Unicode characters and I'm having a bit of trouble. If I try to include a Unicode character like this:
$ echo ☢ | hexdump -C
00000000 e2 98 a2 0a ...
4
votes
2answers
724 views
Passing arguments with quotes and doublequotes to bash script
At this moment I have:
#!/bin/bash
screen -p 'ScreenName' -x eval 'stuff '"'"$@"'"'\015'
echo eval 'stuff '"'"$@"'"'\015'
But when I call my script as:
# script.sh asd "asd" 'asd'
my arguments ...
4
votes
2answers
85 views
Quoting in a function results in error
How should I write the command variable to get the expected behavior?
#!/bin/bash
function f ( )
{
echo "$2"
}
command="f --option=\"One Two Three\" --another_option=\"Four Five Six\""
$command
...
4
votes
2answers
137 views
How can I use column to delimit on tabs and not spaces?
I'd like to use Unix column to format some text. I have fields delimited by tabs, but within each field there are also spaces. column delimits on white space (tabs and spaces). How can I make column ...
4
votes
2answers
97 views
Is there any reason to escape a dot in a bash filename expansion?
I am working with a bash script that someone else wrote and I see the following line:
cp -v ${LOG_DIR}/${APPLICATION}\.*.log ${ARCHIVED_LOG_DIR}
The files with which it's working are all named ...
4
votes
2answers
144 views
Why am I observing different behaviour of echo?
I am a bash beginner and observed the below behavior of echo
#!/bin/bash
x=" hello"
echo $x
echo "$x"
Now when I run the above code I get
ronnie@ronnie:~$ bash test.sh
hello
hello
...
4
votes
1answer
379 views
How to run this in sudo?
I have this line that I execute from php
sudo -u db2inst1 -s -- "/opt/ibm/db2/current/bin/db2 connect to PLC; /opt/ibm/db2/current/bin/db2 \"update EDU.contact set MOBILE_PHONE = '123'\""
it works ...
4
votes
1answer
354 views
Calling script from bash has problem with arguments
I have a script that generates an xml file and then executes a perl script, passing a series of arguments to it. Here's the key code:
CMD="./dnscurl.pl --keyname $KEYNAME -- -X POST -H ...
4
votes
1answer
148 views
printing a string's “canonical print-escaped form”
I'm trying to write a function, I'll call it escape, that will behave like this:
% IFS=$' \t\n\000'
% escape FOO $IFS
FOO=$' \t\n\000'
In other words, escape takes two arguments, and then, taking ...
3
votes
2answers
70 views
Quoted vs unquoted string expansion
for i in $(xrandr); do echo "$i" ; done
for i in "$(xrandr)"; do echo "$i"; done
for i in "$(xrandr)"; do echo $i; done
I understand why 1 differs from 2. But why does 3 give a different output ...
3
votes
3answers
153 views
Zsh function with su and echo
I'm trying to add a function to my .zshrc that makes adding new USE flags to my /etc/portage/package.use file easier. Normally, I'd have to do
su -c 'echo "net-misc/aria2 bash-completion bittorrent" ...
3
votes
3answers
1k views
Why does bash variable expansion retain quotes?
> echo "hi"
hi
> VAR='echo "hi"'
> $VAR
"hi"
Why is the output of the above commands different?
A similar thing occurs with single quotes:
> VAR="echo 'hi'"
> $VAR
> 'hi'
3
votes
3answers
2k views
Why is echo ignoring my quote characters?
The echo command isn't including the complete text that I give it. For example, if I do:
$ echo ' echo PARAM=` grep $ARG /var/tmp/setfile | awk '{print $2}' ` '
It outputs:
echo PARAM=` ...
3
votes
3answers
294 views
Escaping argument in bash script?
I'm writing a bash script wherein I want to check that one of the arguments passed to it is a valid group.
I have the line
if [ `grep -c -e '\b$2\b' /etc/group` -eq 0 ]; then
echo "Error: $2 is ...
3
votes
4answers
151 views
How to print “$” in here-document
How can I echo "$" in a here-doc in bash?
For example, I want to have a file with the content on remote server like $ABC=home_dir.
$ ssh hostname sudo -s <<EOF
echo "$ABC=home_dir" > file
...
3
votes
2answers
236 views
how to grep for c:\
I'm using cygwin's grep to find all instances of hardcoded paths on c drive.
doing:
grep -r "c:\\" .
gives grep: trailing backslash
Does anybody know how I can do this?
3
votes
2answers
250 views
Read a file and copy to another file
I'm having a issue, I need to copy the file contents and remove a couple of lines if they match the output from a previous command. But so far, I'm having an issue in maintaining the file lines ...
3
votes
1answer
292 views
Difference between ' and " on command line (bash)?
I used to use '' and "" interchangeably on the command line, but I recently noticed that '$HOME/some/dir' is not expanded, while "$HOME/some/dir" is. I searched around a little bit and found that "" ...
