The shell is unix's command-line interface. You can type commands in a shell interactively, or write scripts to automate tasks. Use this tag for questions applying to /bin/sh and most compatible shells (ash, bash, ksh, zsh, …).

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How to copy or read the return value (exit status) from AWK script into the shell script (bash) to be used in if statement to compare

I want to read the error codes or the exit status of awk script into shell to use in if condition to compare for error handling my shell script looks something like: My script: #!/bin/sh awk -v ...
3
votes
3answers
289 views

Split a returned block of text into lines in terminal?

When I give commands like echo $PATH or which program, I often get a very large block of text consisting of may directories. This is fairly useless, if I am for example, looking to see if there is or ...
2
votes
2answers
75 views

Is it secure to connect remotly to Mysql using shell?

I have created a shell script to connect to a DB and do some queries: #/!bin/bash ... ... mysql -h remote -u root --password='pw' MatchingDB some SQL queries My question is : Is this connection ...
45
votes
4answers
4k views

Why does no one use the true Bourne shell as /bin/sh?

I've noticed that basically no system I've ever worked with has /bin/sh as a real executable. It's always a symlink to dash, bash in POSIX mode, or something similar. Why? What are the disadvantages ...
1
vote
1answer
65 views

What can I know about this part of code? [duplicate]

What does this part of a script do? This is a part of a scrpt in bash for j in *.* ; do cp $j ../../$name-S$i.gid/data/${j%%.*}$i.${j#*.} sed "s/$name-S/$name-S$i/" $j > ...
1
vote
0answers
66 views

Why below script is not able to find and delete files [closed]

Why below find command does not find and delete files ? I am launching it like this ./script.sh 1 MYFOLDER days_period=$1 myuser=$(whoami) folder_prefix=$2 LOGS_DIR=~/$folder_prefix/logs if [ $# ...
18
votes
4answers
946 views

Path independent shebangs

I have a script that I want to be able to run in two machines. These two machines get copies of the script from the same git repository. The script needs to run with the right interpreter (e.g. zsh). ...
22
votes
3answers
1k views

If processes inherit the parent's environment, why do we need export?

I read here that the purpose of export in a shell is to make the variable available to sub-processes started from the shell. However, I have also read here and here that "Processes inherit their ...
2
votes
1answer
67 views

Is there a command which creates a temporary file containing the arguments passed to it?

I can paste the contents of a file into a command using cat and backticks: ls `cat filenames` Is there a way to do the reverse - to turn a string into a (temporary) filename? gcc -o cpuburn `uncat ...
4
votes
1answer
122 views

Why do bash variables disappear when I use xargs?

I have a simple bash script and want to count how often a command gets called. Here is a minimal example, the counter is called c and should be 4 at the end: #!/bin/bash c=0; for a in X Y; do for ...
0
votes
1answer
273 views

how to ignore a MySql error and go on to the next query?

I have created a shell script to connect to a DateBase and INSERT IPs and MACs from dhcpd.log file by connecting to the DB only once: #/!bin/bash dhcpLogFile="/var/log/dhcpd.log" NumberOfLines=$(awk ...
2
votes
1answer
202 views

how to Connect to Mysql only once?

I have created a shell script to connect to a DB and INSERT IPs and MACs from dhcpd.log file the scripts worked properly: #/!bin/bash #Defining Variables dhcpLogFile="/var/log/dhcpd.log" #Begin Code ...
2
votes
3answers
109 views

Script needs to read echoed line

So, I need to write a Bourne-shell script, where my script has to work with the line, that was just echoed to stdout - e.g.: echo *something* | myscript.sh [parametres...] This may be a basic ...
0
votes
2answers
543 views

Bad configuration option: ControlPersist while scp with control master?

I am using SCP with ControlMaster to copy the files but somehow I am getting this error back - command-line: line 0: Bad configuration option: ControlPersist command-line: line 0: Bad configuration ...
3
votes
2answers
2k views

find the single largest file

We host a share of size 4 TB. How efficient is it to find a file with highest size. Usually we use: du -ak | sort -k1 -bn | tail -1 and it is not easy to scan through a share of such huge size and ...
0
votes
1answer
150 views

Using the Echo Command with Sleep command

So I asked a question on here a few weeks ago and the response I got was helpful but I figured I would add some info to get a better response. I work with a computer system that has 8 servers (4 ...
2
votes
1answer
84 views

How do I eval two commands?

If I run this: echo "echo 'a'; echo 'b'" It produces a string which I can then run, and it works - echoes a\nb\n. However, this does not work: $(echo "echo 'a'; echo 'b'") Why not? It doesn't ...
0
votes
1answer
105 views

What is the :0 terminal in the who command's output? [duplicate]

When I type who in my console terminal, I get the following output: hubert :0 2014-05-16 21:40 (:0) hubert pts/0 2014-05-16 21:46 (:0) From info who I know that both :0 and ...
28
votes
5answers
1k views

To env or not to env

What is the difference between the command $ env FOO=bar baz and $ FOO=bar baz What effect does env have?
1
vote
1answer
109 views

rsync parallel vs serial transmissions

Using Bash 4 and rsync on RHEL 6, are there any differences between the following methods? If so, which is more efficient, and what are the differences between these 3 methods: 1) rsync -avz ...
3
votes
0answers
65 views

Some puzzles of how to close file descriptors on sh or bash [duplicate]

Question 1. What will happen if we close a input file descriptor as if it is a output file descriptor? (or vice versa). For Example, $ exec 5<&2 $ exec 5>&- In my linux box, ...
2
votes
1answer
176 views

How to find text in files and only keep the respective matching lines using the terminal on OS X?

I am pretty new to the terminal and command lines, from what I have found out grep seems to be the right tool for search files for specific text strings. I have a folder with many huge text files and ...
5
votes
3answers
3k views

stdin, stderr, redirection and logs

Is there a difference between those two lines ? /home/user/script.sh >> /home/user/stdout_and_error.log 2>&1 /home/user/script.sh 2>&1 >> /home/user/stdout_and_error.log ...
2
votes
2answers
40 views

How can I automatically create a document that allows me to compare a list of 4 .png files side-by-side?

So I have a list of 4 .png files, and I'd like to auto-pipe this to some document that puts them all side-by-side for easy comparison. I'm thinking of automatically putting them in a HTML file. So ...
0
votes
3answers
179 views

How to delete number of lines from file repetitively

I've read How do I delete the first n lines of an ascii file using shell commands?, it is helpful. However I've a file something as below (please consider 2 columns as 2 different files): 1 4 1 4 1 4 ...
2
votes
2answers
144 views

AIX shell script compiler

I know it sounds strange, but is there a good tool that compiles a shell (.sh) script into a executable format? I want to protect the script in such a way it will not be modified by someone. Thanks
5
votes
1answer
207 views

Where is $_ defined by POSIX?

In the comments to the accepted answer to this Unix & Linux StackExchange question, it is stated that $_ is "one of only some 7 special parameters defined by POSIX". I can't find that definition ...
1
vote
2answers
87 views

Renaming a whole folder content

I'm on OSX 10.9.2 (BASH 3.5) and I wanted to rename a whole folder content names. So I run a script and somehow ended with this: s01eDavid.Letterman.2014.02.27.Stupid.Human.Tricks.x264-SWOLLED.mp4 ...
1
vote
1answer
50 views

check if genisoimage is succesful

I use a script to convert all VIDEO_TS directories to .ISO. How can I check if genisoimage is actually converting it instead of it failling and converting the next folder? After conversion I have a ...
36
votes
5answers
47k views

How to monitor CPU/memory usage of a single process?

I would like to monitor one process's memory / cpu usage in real time. Similar to top but targeted at only one process, preferably with a history graph of some sort.
2
votes
1answer
3k views

curl url call in for loop? [closed]

I am working with bash and I am trying to make a curl url call in a for loop. Below is my simple curl call - curl -v --header "Connection: keep-alive" ...
0
votes
1answer
42 views

understand if a shell process is in background?

I keep an instance of mutt idling on a terminal, if it is on index or pager I want it to be able to receive a macro from an external process (AutoKey or xdotool etc..), but the external program need ...
1
vote
2answers
116 views

Why we can not see a single hyphen from $0 on a login shell invoked with `--login` option?

man bash says, A login shell is one whose first character of argument zero is a -, or one started with the --login option. When we invoke a terminal such as mintty - on Cygwin, we can see a ...
6
votes
4answers
3k views

Why doesn't grep using pipe work here?

I have the following command: find / -name libGL.so.1 Which returns lots of lines with "Permission denied". I want to exclude such lines, so I added the following: find / -name libGL.so.1 | grep ...
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3answers
136 views

Why doesn't my command work when aliased?

I use ps -ef | grep catalina | grep -v grep to print the tomcat process running on the system: kshitiz 7099 1 0 May11 ? 00:02:29 /usr/lib/jvm/jdk1.8.0/bin/java ...
1
vote
2answers
334 views

Variable value is not recognized after using gnu parallel?

I have a below shell script from which I am trying to copy 5 files in parallel. I am running my below shell script on machineA which tries to copy the file from machineB and machineC. If the file is ...
46
votes
6answers
44k views

How do you move all files (including hidden) in a directory to another?

How do I move all files in a directory (including the hidden ones) to another directory? For example, if I have a folder "Foo" with the files ".hidden" and "notHidden" inside, how do I move both ...
0
votes
1answer
49 views

Set alias which doesn't send specified text? [closed]

EDIT I set a alias task in ~/.bashrc. The following: alias join="clear; screen -ls; screen -rx [<ID_OF_THE_RUNNING_SCREEN> quit]" If i the task join is executed, the following has to ...
1
vote
2answers
123 views

How to properly launch a program and make possible to redirect its running output (stdout and stderr) at a later stage?

The problem is quite simple: I find useful to have the possibility to switch on (and off) the output of some running program in each moment I need. To be more precise I want to be free to redirect ...
0
votes
4answers
180 views

What's the difference between $@ and $* [duplicate]

According to this page, $@ and $* do pretty much the same thing: The $@ holds list of all arguments passed to the script. The $* holds list of all arguments passed to the script. After searching ...
3
votes
1answer
458 views

Prevent hanging of “echo STRING > fifo” when nothing is reading that FIFO

When I echo something to a named pipe made with mkfifo, it hangs if no process is reading from that pipe. How can I prevent that, i.e., stop that from hanging? And by the way, why is that hanging ...
0
votes
1answer
41 views

Is there a way to make git commit have -v as a default?

I have git () { [ $1 = commit ] && command git commit -v "${@:2}" || command git "$@"; } It makes git commit have -v as a default, otherwise pass on the params and do whatever the git ...
1
vote
3answers
70 views

File comparing and appending based on fields

I want to compare 2 files, locus_file.txt is a very large file and atrr.txt is a small file. I want to match the first 2 columns of the first file to the second column of atrr.txt and print the ...
2
votes
1answer
622 views

How to automatically launch a lxc container on ssh connection?

I'm attempting to setup a system that automatically creates a new sandbox on a ssh login to use as a temporary jump box into my server. So to do this I was wonder how to setup lxc to spin up a new ...
0
votes
4answers
763 views

Why does this shell script fail in bash, but the commands work in SSH?

I'll first admit to being quite the noob in Linux/SSH/etc. What I'm trying to write is a shell script that will back up a website and all the MySQL DBs that support it. I found examples all over the ...
0
votes
1answer
559 views

Escaping multiple backticks in a sed call

I need to perform search and replacement iteratively in several SQL statements: From: CREATE TABLE `Old_Name` ( To: ALTER TABLE `Old_Name` RENAME TO `New_Name` The above query contains ...
1
vote
2answers
728 views

“emacs: standard input is not a tty” when starting Emacs at login

I have Fedora 20 and Gnome3 classic, and I am trying to use the CTRL/ALT/Fn terminal windows. When I want to edit a file with emacs I use the following script so that my Hints file is automatically ...
4
votes
2answers
153 views

Running several times the same command with several aguments after a pipe

I have a key (of random binary data) that gets generated by get_key. And with this key, I can do several things with my encrypted files. For example, I can decrypt them. get_key | tee >(decrypt ...
0
votes
1answer
106 views

How use `rsync -R` with multiple subdirs or install -D with multiple files?

Is possible with rsync to copy multiple files from a source directory to a dest directory with multiple subdirectories that don't exist? Or use install -D with multiples files to a directory that ...
5
votes
3answers
471 views

How can I background a shell script during a Kickstart?

I have a Red Hat Kickstart process which reports its progress at key points via a POST request to a status server. This is fine during %pre and %post, but when the actual build is taking place ...