Questions tagged [bash-scripting]
Bash scripting is making scripts in the Bash shell language.
955
questions
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votes
3
answers
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ZSH: Read command fails within bash function "read:1: -p: no coprocess"
Edit:
Seems to work within bash. It appears the problem is related to zsh. If there is a better site to post this issue on let me know.
I am writing a simple script that creates a series of ...
- 1,097
65
votes
4
answers
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views
how to grep and print the next N lines after the hit?
I would like to grep for an occurrence in a text file, then print the following N lines after each occurrence found. Any ideas?
- 4,427
50
votes
10
answers
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views
Suppress execution trace for echo command?
I'm running shell scripts from Jenkins, which kicks off shell scripts with the shebang options #!/bin/sh -ex.
According to Bash Shebang for dummies?, -x, "causes the shell to print an execution trace"...
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40
votes
2
answers
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views
How can I compare a variable to a text string, rather than integer, in an if/else statement?
In the process of writing a shell script, I ran into an issue with the following if/else statement that falls somewhere in the middle of the script:
if [ $act -eq "add" ]
then
read - "add or ...
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36
votes
1
answer
11k
views
Bash: optionally passing arguments to a command
I'm trying to add arguments to a command call depend on another variable. Please look at the shell scripting code:
curl \
$([ -z "${title}" ] || echo --data-urlencode title=${title}) \
http://...
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32
votes
5
answers
61k
views
Passing two arguments to a command using pipes
Usually, we only need to pass one argument:
echo abc | cat
echo abc | cat some_file -
echo abc | cat - some_file
Is there a way to pass two arguments? Something like
{echo abc , echo xyz} | cat
cat ...
- 1,753
30
votes
1
answer
5k
views
What is <<!END in a Bash script?
Consider:
#!/bin/bash
/u01/app/oracle/middleware/oracle_common/common/bin/wlst.sh <<!END
connect('user','pw');
p=redeploy('application');
p.printStatus();
exit();
!END
The above script is ...
- 411
29
votes
2
answers
59k
views
Replace backslash("\") with forward slash("/") in a variable in bash
I want to replace backslash(\) with forward slash(/) in a variable in bash.
I tried it like this, but it doesn't work:
home_mf = ${home//(\)//(/)}
For example, I would like
\a\b\c -> /a/b/c
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26
votes
3
answers
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views
How to update bash on Mac OS X Yosemite
Just trying to learn bash scripting a little.
My old bash version:
Bash version 3.2.53(1)-release...
I've updated my bash on mac os x yosemite with homebrew:
brew update
brew install bash
Then in ...
- 2,157
25
votes
4
answers
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views
Is it safe to open a file that is being written by a running script?
I am running a shell script that is writing to a file.
This script may take a long time to complete and I would like to monitor the partial output rather than wait for the whole script to finish.
Is ...
- 559
23
votes
4
answers
98k
views
Edit xml file using shell script / command
I need to do this using unix script or command
There is a xml file in /home/user/app/xmlfiles like
<book>
<fiction type='a'>
<author type=''></author>
</...
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23
votes
2
answers
9k
views
Writing shell scripts that will run on any shell (using multiple shebang lines?)
I've just started getting deeper into shell scripting, and I've always just thrown my script in a file, marked it chmod +x and then done /path/to/script.sh and let whatever interpreter is the default ...
- 365
20
votes
1
answer
28k
views
Howto switch / chage user id witin a bash script to execute commands in the same script?
Is there a way to switch user identity within a script (executed as root as part of an installation process) to execute some commands without calling an external script, then return to root to run ...
- 365
19
votes
4
answers
13k
views
appending timestamp to tail -f results
I would like to have a timestamp printed in front of every line that comes out of a "tail -f outputfile", so that I know when is each line printed in. Something like:
[...]
20110617_070222:results ...
- 4,427
17
votes
2
answers
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views
Properly escaping forward slash in bash script for usage with sed
I'm trying to determine the size of the files that would be newly copied when syncing two folders by running rsync in dry mode and then summing up the sizes of the files listed in the output of rsync.
...
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17
votes
3
answers
12k
views
Prefix to each output of a command on runtime
I am trying to make a modular script. I have several scripts/commands which are called from a single script.
I want to prefix the output of each separate command.
Examle:
My files are allcommands.sh ...
- 301
17
votes
4
answers
27k
views
How to truncate file by lines?
I have a large number of file, some of which are very long. I would like to truncate them to a certain size if they are larger by removing the end of the file. But I only want to remove whole lines. ...
- 529
15
votes
2
answers
20k
views
Write n bytes from a file into another in Bash
Hello how can I write n bytes from one file into a new file starting from the k position using Bash?
For example if n=60, k=1 and file size=100 then: the 2nd file would consist of from the 1st byte ...
- 151
14
votes
3
answers
5k
views
why doesn't a bash while loop exit when piping to terminated subcommand?
Why doesn't the command below exit? Rather than exit, the loop runs indefinitely.
While I discovered this behavior using a more complex setup, the simplest form of the command reduces to the ...
- 373
14
votes
2
answers
12k
views
bash completion for filename patterns or directories
I'm trying to get a bash completion script set up and having some trouble.
I would like to set it up so the completions listed are either files matching a particular extension, or directories (which ...
- 243
13
votes
3
answers
27k
views
Process each line of a file in bash
When I want to do something with each line in a file I usually write
cat my_file | while read a
do
gzip "$a"
done
The gzip is just an example it can be anything.
What I'm wondering is if there is ...
- 34.5k
13
votes
3
answers
15k
views
How get full path to target of link
If I have a symbolic link /var/opt/foo created with ln -fs /path/to/target/dir foo. How can I in a script that sees only the link get /path/to/target/dir?
What I want to achieve in the script is rm -...
- 34.5k
13
votes
6
answers
62k
views
awk / sed to print only up to the underscore character
How can I use awk or sed to print a string only up to the first underscore character?
Before:
host100_044 2
host101_045 2
host102_046 2
After:
host100
host101
host102
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12
votes
2
answers
3k
views
Difference when using backticks in double quotes and single quotes in Bash
Why to the following two executions differ in output? (I need double quotes for variables in my eventual command)
$ sudo su -c "echo `cat /root/root_file`"
cat: /root/root_file: Permission denied
$ ...
- 385
12
votes
2
answers
20k
views
Is there a way to pass arguments via pipe on bash?
Is there any way to pass arguments via pipe on bash?
something like:
echo value1 value2 | mkdir -p ./$1/$2
The line above would create the directories ./value1/value2
If this is not possible I ...
- 133
12
votes
1
answer
11k
views
Linux: How does file modification time affect directory modification time and directory access time?
I would like to learn more about how file access time and file modification time related to directory access and modification times.
I did read the "questions allowed here" but if there is a better ...
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11
votes
4
answers
14k
views
how to properly use $1 in an alias with two arguments
i have to compare a number of files and I don't want to change the command in two places all the time. so i want to create an alias in bash.
alias gd='gvimdiff $1 dir/$1'
so that i can get
...
- 1,318
11
votes
4
answers
4k
views
How to properly restore settings when running a script using "source"?
I'm writing a script that needs to be executed using source, because its task is to modify the environment. During the script, I want to use set -e so that any error stops the script. The script looks ...
- 3,173
11
votes
2
answers
30k
views
How do I concatenate strings from a list in a bash script?
As an example:
List="A B C D"
for I in $List
do
OUT=$OUT" -$I"
done
When I run this the result is:
" -A -B -C -D"
but want it to be:
"-A -B -C -D"
How do I concatenate without the leading ...
- 213
11
votes
2
answers
20k
views
How to get list of all child process spawned by a script
Context:
Users provide me their custom scripts to run. These scripts can be of any sort like scripts to start multiple GUI programs, backend services. I have no control over how the scripts are ...
- 221
10
votes
3
answers
20k
views
how to gzip and scp at the same time
I have a file in which i wanted to zip up and at the same time transfer over to another host using scp.
I tried to do the following command but failed. I do not mind zipping up and scp over later, ...
- 1,625
10
votes
1
answer
3k
views
Get bash to respect quotes when word splitting subshell output
I have a command that outputs some parameters that I want to pass to another command. However, when I run the command in a subshell, the output is subject to word splitting unless I quote the whole ...
- 2,493
10
votes
1
answer
12k
views
How to change/add a tracker to a .torrent file using the command line?
I use transmission-daemon on Debian for my torrents.
For now, I've been using the website http://torrenteditor.com/ to add trackers to .torrent files.
I'd like to edit .torrent files directly using ...
- 309
9
votes
3
answers
55k
views
Insert quote into string variable in bash
Is there way of inserting a quote at the start and end into a string variable?
I have this variable say:
string="desktop/first folder"
If I echo this, it will display:
desktop/first folder
I need ...
- 93
9
votes
1
answer
36k
views
cp: cannot stat '/some/path/*': No such file or directory
My script code is:
var="/some/path"
cp "$var*" "/another/path"
Then it throws:
cp: cannot stat '/some/path/*': No such file or directory
I have tried this and got the same error:
cp "${var}*" "/...
- 93
9
votes
2
answers
17k
views
Use "read" in Bash script with a standard answer
How can I use read with something as standard response, which the user can change though? (a default answer)
- 101
9
votes
2
answers
7k
views
Which bash rc files are run on non-interactive/non-login shells?
My Understanding
there are no rc files called for non-interactive/non-login shells; for example, those run by cron
(I don't know this for certain and would lean on the community's expertise)
non-...
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votes
1
answer
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views
Automated Interaction with Google Chrome
All right SU, I have a fun nut to crack.
I have 8 screens set up in a line, all hooked into one beefy G5 running Snow Leopard (yes, 4 graphics cards; about 15,000 pixels wide!). I am setting up a ...
- 1,569
8
votes
3
answers
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views
What commands would I use to create two child processes serially?
I want to spawn two child processes, but wait until the first reaches a certain point in its execution (which can be determined by examining stdout) before spawning the second. I'm not sure which unix ...
- 205
8
votes
1
answer
3k
views
How to make sed omit not matching lines?
In the following example, sed matches lines starting with an a or a c and prints the first character of that line (a or c):
$ echo "ag
bh
ci
dj
ek
fl" | sed 's/\(a\|c\)./\1/' # Matches lines starting ...
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8
votes
3
answers
8k
views
Bash: better way to output to both console and output file than tee?
What I need to display is a log refreshing periodically. It's a block of about 10 lines of text. I'm using |tee and it works right now. However, the performance is less satisfying. It waits a while ...
- 141
8
votes
1
answer
10k
views
Bash script to toggle monitor input from HDMI to DisplayPort and vice-versa
I use ddcutil as a command line alternative to physically pressing the buttons on my monitor to change input from HDMI to DisplayPort, and have it initially set it up to switch from one to the other ...
- 93
8
votes
3
answers
22k
views
how can sed get patterns from a file
I have two files one holds a list of patterns, another need to be changed based on these patterns.
So far I have been experimenting with
cat patterns.txt| xargs -n1| sed 's/patternfromfile/...
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8
votes
5
answers
7k
views
Delete all files (except the four newest) throughout directories using a Bash script
I'm looking for a Bash script that will go into a list of directories and delete all but the four most recently created files.
How can I do this?
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7
votes
1
answer
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views
tmux - get pwd of another pane in a bash script?
Is there anyway to find out information about the current working directory of any pane from within a tmux session?
I'd like to write a bash script that changes the directory of the current pane to ...
- 3,056
7
votes
1
answer
23k
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Bash script: "[[: not found"
This is my code:
#!/bin/bash
if [[ -d ~/viwiki ]]; then
cd ~/viwiki
else
mkdir ~/viwiki
cd ~/viwiki
fi
if ! [[ -d ./log ]]; then
mkdir log
mkdir log/log
mkdir "log/wget"
elif ! [[ -d ./log/log ]...
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7
votes
1
answer
5k
views
Cannot resize tmux pane from bash script
Background and Problem:
I have created a tmux script to open a few windows. It works great but then I wanted to place a vertically split pane on one window and resize it to 5 characters tall. I ...
- 193
7
votes
5
answers
4k
views
How to move all sibling folders into one folder?
I apologize that this seems like such a dumb question, but I can't afford to screw it up.
I have a bunch of folders like so:
/users/me/foo/oops1
/users/me/foo/oops2
/users/me/foo/oops3
/users/me/foo/...
- 301
7
votes
2
answers
3k
views
'while read' loop through lines in text file losing characters in Bash script. is FFmpeg line to blame?
I am looping through a text file, using 'while read'. I read three variables from each line - two filenames and a decimal number. I know that this works in a vanilla setup (loop, read line, echo line, ...
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7
votes
3
answers
615
views
Why some commands don't take input redirection?
For example, echo:
[aesteban@localhost ~]$ cat tmp.txt
Angel
[aesteban@localhost ~]$ echo < tmp.txt
[aesteban@localhost ~]$
As you can see, the output is just a blank line. According to my ...
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