I was working my way through a primer on Shell (Bash) Scripting and had the following doubt :
- I came across the
lscommandThe
manpage oflslists a few use cases as :
ls -a
ls --block-size='M'
My Question :
- What is the difference in
-and--?- Why are there 2 nomenclatures used ?
- What is the motivation behind it ?
Long-form (--foo) options are a GNU extension -- something present in GNU ls, but not present at all in the POSIX standard setting requirements for UNIX tools, so other versions of ls are not obliged to support these options. The entire word (foo) is meaningful in this case. This nomenclature was added more recently, and is more expressive than the short form (and doesn't have namespace limitations).
Short-form options (-al) are, at least in form, standardized (though extensions can add new ones). They're handled character by character, one letter at a time -- so -al means -a (show hidden files) and -l (long output), rather than having -al have its own meaning in this case. This is the original syntax for UNIX command-line options, and is thus supported not only for terseness but also for backwards compatibility.
linux,multithreading,linux-kernel
Unlike Windows, Linux does not have an implementation of "threads" in the kernel. The kernel gives us what are sometimes called "lightweight processes", which are a generalization of the concepts of "processes" and "threads", and can be used to implement either. It may be confusing when you read kernel code...
Executable files may be scripts (in which case you can read the text), or binaries (which are ELF formatted machine code). Your shell script is a script; git is an ELF binary. You can use the file command to see more detail. For example, on my nearest Linux system: $...
Checking file and/or directory existence To check whether a file exists in bash, you use the -f operator. For directories, use -d. Example usage: $ mkdir dir $ [ -d dir ] && echo exists! exists! $ rmdir dir $ [ -d dir ] && echo exists! $ touch file...
A workaround is to modify the sudoers file and remove the requirement of a password from your user ID for a particular script to have sudo privileges. Enter sudo visudo After this, add the details in the following manner. username ALL=(ALL) NOPASSWD: /path/to/script Another method would be to pipe the...
I found the discussion in Valgrind mail list when someone had the same problem. The issue was that the kernel have been patched with PaX patches, one of which doesn't allow to look at the /proc/pid/maps. The quote about the patch from wikipedia The second and third classes of attacks...
linux,shell,command-line,awk,sed
Almost same as the other answer, but printing 0 instead of blank. AMD$ awk -F, 'NR>1{a[$2]+=$3;b[$2]++} END{for(i in a)print i, a[i], b[i]}' File pear 1 1 apple 2 3 orange 0 1 peach 0 1 Taking , as field seperator. For all lines except the first, update array a. i.e...
Assuming that your document is well-formed, i.e. <b> opening tags always match with a </b> closing tag, then this may be what you need: sed '[email protected]<[/]\?b>@\n&\[email protected]' path/to/input.txt | awk 'BEGIN {buf=""} /<b>/ {Y=1; buf=""} /<\/b>/ {Y=0; print buf"</b>"} Y {buf = buf$0} ' | tr -s ' ' Output: <b>data1</b>...
python,bash,environment-variables
After updating your .bashrc, perform source ~/.bashrc to apply the changes. Also, merge the two BONSAI-related calls into one: export BONSAI=/home/me/Utils/bonsai_v3.2 UPDATE: It was actually an attempt to update the environment for some Eclipse-based IDE. This is a different usecase altogether. It should be described in the Eclipse help. Also,...
linux,shell,sed,grep,pattern-matching
The -v option to grep inverts the search, reporting only the lines that don't match the pattern. Since you know how to use grep to find the lines to be deleted, using grep -v and the same pattern will give you all the lines to be kept. You can write...
With sort afile > afile this happens: The shell opens and truncates afile because of the file direction operation > afile The shell executes the sort program with one argument, afile, and binds stdout of the new process to the file descriptor opened in step 1. The sort program opens...
As indicated in the comments, you need to provide "something" to your while loop. The while construct is written in a way that will execute with a condition; if a file is given, it will proceed until the read exhausts. #!/bin/bash file=Sheetone.txt while IFS= read -r line do echo sh...
You can use this awk command awk -F, '{if (split($1, a, " ") > 2) print $NF; else print}' file This will output rosario escuela estadist, medellin medellin If you want to get rid of the space before $NF, use this awk command awk -F, '{if (split($1, a, " ")...
The output from set -x uses single quotes. So the outer double quotes were replaced with single quotes but you can't escape single quotes inside a single quoted string so when it then replaced the inner double quotes it needed, instead, to replace them with '\'' which ends the single...
Please save following awk script as awk.src: function date_str(val) { Y = substr(val,0,4); M = substr(val,5,2); D = substr(val,7,2); date = sprintf("%s-%s-%s",Y,M,D); return date; } function time_str(val) { h = substr(val,9,2); m = substr(val,11,2); s = substr(val,13,2); time = sprintf("%s:%s:%s",h,m,s); return time; } BEGIN { FS="|" } # ## MAIN...
Use svn ps svn:externals svn://hostname/branchname -F extenals.txt http://svnbook.red-bean.com/en/1.8/svn.ref.svn.c.propset.html...
linux,windows,sockets,network-programming,raspberry-pi
InputStream input = client.getInputStream(); BufferedReader in = new BufferedReader(new InputStreamReader(input)); Your problem is here. You can't use multiple inputs on a socket when one or more of them is buffered. The buffered input stream/reader will read-ahead and 'steal' data from the other stream. You need to change your protocol so...
.* is greedy: it matches all possible characters. This way, even sed 's/<?php.*//' file will also delete all the content in your file. To prevent this greediness of .*, say "everything but a ?" -> [^?]*: sed 's/<?php[^?]*?><?php[^?]*?>//' file Test $ cat a <?php echo 'first' ?><?php echo 'second' ?><?php...
With GNU grep: grep -oP 'aaa&\K.*' file Output: 123 456 \K: ignore everything before pattern matching and ignore pattern itself From man grep: -o, --only-matching Print only the matched (non-empty) parts of a matching line, with each such part on a separate output line. -P, --perl-regexp Interpret PATTERN as a...
php,bash,drupal,terminal,macports
Do not modify files in /usr/bin. That's Apple's turf, and there are always other possibilities to avoid changing things there, especially since Apple's next update will happily revert these changes again and scripts might rely on /usr/bin/php being exactly the version Apple shipped with the OS. Put the original binary...
This is usually a sign that you should update your mono. Older mono versions have issues with their unzip implementation
Simply, add it in your .bashrc like: alias gl10="gitLog 10" To apply the changes: source ~/.bashrc...
Here's a sed version: /^Host_Alias/{ # whenever we match Host_Alias at line start : /\\$/{N;b} # if backslash, append next line and repeat s/$/,host25/ # add the new host to end of line } If you need to add your new host to just one of the host aliases, adjust...
The problem is, you don't have debug info for the ptr type, so gdb treats it as integer. You can examine its real contents using: (gdb) x/a &ptr 0x600124 <ptr>: 0x7fffffffe950 (gdb) p/a $rsp $3 = 0x7fffffffe950 Of course I have a different value for rsp than you, but you...
linux,vagrant,backup,virtual-machine,sync
Vagrant doesn't inherently support this, since it's intended audience is really development environments. It seems like you're looking for something more like what VMWare vSphere does.
Your variable is still within single quote hence not getting expanded. Use: sed -i 's|^\('"$CHECK"' = \)*.|\1'6'|' /user/file.txt ...
If you want to redirect the normal standard input of the program, you could use so called "here documents" (see e.g. the BASH manual page): java -jar script.jar <<EOF your input here EOF That means standard input (a.k.a. stdin) is redirected and will be the text in the "here document",...
You can achieve that by using the env utility: timeout 10 /usr/bin/env LD_LIBRARY_PATH=/path/to/mod/libc/ cp a b Env will set the environment variable and exec the other utility with that environment....
awk cannot look ahead so you'll have to save the lines. awk 'NR>2{if(z!="")print z;z=y;y=x;x=$0}' file Practically zero memory overhead...
It looks like you're missing zlib; you'll want to install it: apt-get install zlib1g-dev I also suggest reading over the README and confirming you have all other dependencies met: https://github.com/dccmx/mysqldb/blob/master/README Also, I suggest using mysqlclient over MySQLdb as its a fork of MySQLdb and what Django recommends....
Let's look to the POSIX specification to understand why this behaves as it does, not just in bash but in any compliant shell: 2.10.2, Shell Grammar Rules From rule 7(b), covering cases where an assignment precedes a simple command: If all the characters preceding '=' form a valid name (see...
php,linux,apache,logging,permissions
I'd simply set its owner to apache user. This will give you the name of apache user : ps aux | grep httpd In my case (CentOS), it's 'apache' but sometimes it's 'www-data'... chown apache:apache /var/log/httpd/php_errors.log chmod 600 /var/log/httpd/php_errors.log ...
as you see, in Edit1, you (make) try to run JavaScriptCore-4.0.gir instead of compile it with g-ir-compiler; I tried on my pc and my command is: cd /home/davide/src/webkitgtk-2.8.3/build/Source/JavaScriptCore && \ /usr/bin/g-ir-compiler /home/davide/src/webkitgtk-2.8.3/build/JavaScriptCore-4.0.gir \ -o /home/davide/src/webkitgtk-2.8.3/build/JavaScriptCore-4.0.typelib as a workaround, you cand edit: build/Source/JavaScriptCore/CMakeFiles/JavascriptCore-4-gir.dir/build here's the lines on my file (the last...
linux,linux-kernel,kernel,linux-device-driver,system-calls
The ret_from_syscall symbol will be in architecture-specific assembly code (it does not exist for all architectures). I would look in arch/XXX/kernel/entry.S. It's not actually a function. It is part of the assembly code that handles the transition from user-space into kernel-space for a system call. It's simply a label to...
Using sqlite3 from bash on OS X seems fairly straightforward (I'm no expert at this, by the way). You will need to find out which table you need. You can do this with an interactive session. I'll show you with the database you suggested: /Users/fredbloggs> sqlite3 ~/Library/Application\ Support/Dock/desktoppicture.db SQLite version...
Try this to create a string variable n, with no leading whitespace (thanks @011c): n="10.0.0.135.527" wget http://infamvn:8081/nexus/content/groups/LDM_REPO_LIN64/com/infa/com.infa.products.ldm.ingestion.server.scala/"$n"-SNAPSHOT/com.infa.products.ldm.ingestion.server.scala-"$n"-20150622.210643-1-sources.jar ...
bash,shell,curl,command-line,pipe
Try this: curl --silent "www.site.com" > file.txt ...
What I have tried sed 's/[a-z],[a-z]/[a-z], [a-z]/g' <<< "suny stony brook, stony brook,usa." You need to use regex's capture groups here to refer to the original [a-z] values. For example: s/\([a-z]\),\([a-z]\)/\1, \2/g Notice how I've surrounded those [a-z] with \( and \)? These form capture groups that can be...
You can create an alias: alias php="php55" Now if you type php it uses php55...
I would simply start the tail in background and the python process in foreground. When the python process finishes you can kill the tail, like this: #!/bin/bash touch /tmp/out # Make sure that the file exists tail -f /tmp/out & pid=$! python test.py kill "$pid" ...
You don't need the quotes. Just use ${i}, or even $i: pomme[${i}]="" Or pomme[$i]="" ...
I would store the output of find, and if non-empty, echo the line break: found=$(find . -name "${myarray[i]}") if [[ -n $found ]]; then { echo "$found"; echo "<br>"; } >> "$tmp" fi ...
Assuming you want to replace the word 'apple' with 'banana' (exact match) in the contents of the files and not on the names of the files (see my comment above) and that you are using the bash shell: #!/bin/bash COUNTER=0 for file in *.txt ; do COUNTER=$(grep -o "\<apple\>" $file...
In Bash 4 you can use parameter expansion directly to capitalize every letter in a word (^^) or just the first letter (^). for f in *; do mv -- "$f" "${f^}" done You can use patterns to form more sophisticated case modifications. But for your specific question, aren't you...