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====Bash Quick Tips====

Here is a list of oneline tips for [[Bash]] commands linked to phrases.

**The X File** (Written by Martin Streicher)
To run X clients securely, use ssh -Y host. DISPLAY is automatically set to encrypt and tunnel X protocol back to the X server.

**Rename With Impunity**
Do you need to change the extension of many files at a time? Nothing is faster than zsh -c "autoload zmv; noglob zmv -W *.a *.b".

**Jump Back** (Written by Aram Yegenian)
To go back to the last directory you visited, simply type cd -. (Thanks to Aram Yegenian)

**Contract Killer**
Want to kill a process the quick and easy way? Try killall /path/to/file, which kills all processes executing /path/to/file.

**Shred a File**
To delete a file securely, first overwriting its contents (25 times), run shred -u -z -v file.

**Expire Passwords**
Improve system security by expiring user passwords from time to time. The command passwd -x 30 joe forces joe to change his password after thirty days.

**Directories Made Easy**
Use mkdir -p to create a hierarchy in one fell swoop. For example, mkdir -p a/b/c/d makes directory d in directory c in directory b in directory a.

**Group-ies**
To see the list of groups you're a member of, use id -Gn. id has effectively replaced groups and whoami.

**What Timezone Is It?**
If you want to know the proper name of your current time zone, run the interactive command tzselect. Follow the prompts and use the output in your shell login file.

**Faster, Simpler Version Control**
Tired of CVS? Try [[http://darcs.net/ darcs]]. Creating a repository with darcs is as easy as cd ~/myproject; darcs init; darcs add -r *. Use apt-get install darcs to install or see the [[http://wiki.darcs.net/ darcs wiki]] for source, tools, and more info.

**Watch, Again** (Written by Thomas Materna)
Reader Thomas Materna says: If you use watch to monitor the output of a command that contains wildcards, enclose the command in quotes so the expansion is made every time. For example, watch "ls *.gz" shows new *.gz files as they're created, whereas watch ls *.gz only shows the *.gz files that exist at the moment you run watch.

**A Smart Man** (Written by Håkon Karsten Eide)
If you want to look at a compressed log file (.gz), use man. For example, man ./auth.log.1.gz shows the contents of the log file. (Thanks to Håkon Karsten Eide.)

**Look at Files in Reverse**
To look at a log in reverse (most recent events first), run tac logfile | less. tac reverses the lines of any file. Use tac - to read from stdin.

**Move Wisely**
If you're not careful, **mv** can overwrite existing files. Move files wisely with mv --backup=existing -v. To save typing, set VERSION_CONTROL to existing.

**Bash Quick Copy** (Written by Steve Fox)
In bash, the command-line incantation cp snark{,.bak} copies snark to snark.bak. (Thanks to Steve Fox.)

**Command Redux**
To run a command again and again and see what's different each time, use the clever watch. For example, watch -d ls -l runs ls -l every two seconds and displays "diffs."

**Spying on "Noisy" Files**
If you move files from other operating systems to Linux, the files may contain odd, unprintable characters. To reveal control characters, non-ASCII characters, and so on, use either cat -e filename or od -c filename.

**Temporary Files Made Easy**
Need a reliable way to choose a unique temporary file? Use **tempfile**. For instance, **tempfile -p martin** creates /tmp/martiOzXxwL with mode 0600.

**Another Fast Backup** (Written by Morvan Bliasby)
To make a fast backup, say, of all system .conf files, combine locate, grep, and zip as in locate .conf | grep /etc/ | zip zipfile -@

**Create a Tarball**
A so-called tarball is a gzip-compressed tar archive. You can create one quickly with tar zcvf tarball.gz files.... To unpack a tarball, use tar zxvf tarball.gz.

**Are You Sure?**
Many commands that affect the file system, such as **ln**, **mv**, and **rm**, have -interactive options (abbreviated by -i). Use -interactive mode to approve each operation.

**Who, What, When?**
Need to know what makes your machine tick? Just type **uname -a** to see your machine's hostname, kernel version number, processor type, and more. Also see the commands arch, hostname, env, kernelversion, and ifconfig.

**Update Debian**
If you use Debian Linux, don't forget to run apt-get update; apt-get upgrade at least once a week to pick up the latest and greatest packages and security patches.

**Tune In the Tube** (Written by Johan Eriksson)
Watch a lot of TV? Tired of missing Most Extreme Elimination Challenge? Reader Johan Eriksson recommends [[http://mtvg.sourceforge.net/ Maxemum TV-Guide]], a free KDE application that browses the television broadcast schedules of several countries.

**Add Users En Masse**
You can quickly create new user accounts or update existing accounts with the **newusers** command. Create a list of accounts in a passwd-like file and run the command newusers file.

**Tee for Two (or Three, Four, ...)**
To watch the output of a command and capture the output in a file, use **tee**. For example, find / -name '*.pm' -print | tee log lets you watch the results and keep the results in log. Use –a to append.

**Links in a Snap**
Use **cp -l** to make links to existing files. You can even use **cp -rl** to create a shadow of an entire directory tree.

**Modes Made Easy**
In addition to octal numeric modes (such as 644), **chmod** also supports a symbolic mode that can set and incrementally add or remove permissions. For example, **chmod g+w** adds group write without changing other permissions, **chmod o-a** removes all permissions for other, while **chmod u=rw** gives read/write permission only to the file's owner (and is the equivalent of setting mode 600).

**Customized File Metadata**
Build your own view of file metadata (permissions, file name, file size, and so on) with the stat command. Use -c (or --format=) to display the fields you want, in the order you want -- perfect for processing with scripts!

**Beware Root**
Avoid logging in as root. Instead, use **sudo** to run individual commands as the superuser. As Spider-man says, "With great power comes great responsibility."
Typically Puppy runs in Root so there is no need to use **sudo**. Some versions have a default user called Spot.

**Which Which is Which?**
If you want to know all of the locations of a particular command in your PATH, use **which -a** command. The result is a list of filenames in PATH order.

**Disable A User Account**
To temporarily disable a user account, run **password -l username**. To re-enable an account, use the **-u** option.

**Process Lookup Made Very Easy**
Need to find or kill a process? Use the utilities **pgrep** and **pkill**. For example, the command **pkill -INT -u root sshd** sends the INT signal to the sshd process owned by root. For puppy 2.10, use menu/control panel/KP manage system processes for a graphical interface to all your processes.

**Easy Parsing**
If you have a comma-delimited file, use cut -s -d, -f n file to extract the nth field from each line of file. The -s option skips lines without the delimiter.

**Less is Much More**
Here's a way to save some typing: pipe the output of a command to less -Ofile, as in find / -name '*.pl' | less -Operlfiles. The option -Operlfiles automatically copies stdin to the file perlfiles.

**Unique Temporary Filenames**
Shell scripts often use temporary files to store transient data. To ensure the novelty of each temporary filename, append a qualifer such as $$, the current process ID, to the filename.

**Compressed File Tools**
View and process a gzip-compressed file (such as an archived log file) without expanding it using zcat, zdiff, zmore, zless, zcmp, zgrep, zegrep, and zfgrep.

**Download from the Command-Line**
**wget** is an invaluable utility. Use it from the command-line or a shell script to download a web page, an entire web site, a tarball, or just about any http: or ftp: URL. wget can also help debug HTTP and FTP connection problems.

**Watch a Log File**
If you want to watch a log file, use **tail -F**. The **-F** option prints new content as it's appended (like -f), but also re-opens a file if it's created anew, as occurs when a log file is rotated.

**Perl One-Liner**
You don't have to know Perl to use Perl. The command-line **perl -p -i -e 's/oldstring/newstring/g' * ** replaces all occurrences of oldstring with newstring in all files in the current directory and makes backup copies of the original files.

**Instant Environment Variable** (Written by Jerry Peek)
If you use bash, you can set an environment variable for a single command by setting the variable before the command, like this: VISUAL=/usr/bin/emacs ci -l foo.txt

**Copy a Directory**
Need to make a verbatim copy of a directory? Use the command (cd /old/directory; tar cf - .) | (cd /new/directory; tar xf -)

**Find Any File Fast**
Need to find a system configuration file but only remember a part of its name? Use locate. It's faster than running find / ... and much simpler to use. (Run **updatedb** often to keep the locate file database up-to-date.)

**Reference the Directory Stack**
If you use **pushd** and **popd** to maintain a directory stack, use ~n on the command-line to reference the nth element of the stack with (where n is 0, 1, 2, and so on).

**Run a Job at Boot**
Written by Martin Streicher
If you want to run a command every time your machine boots, but don't have access to the init scripts, use cron's @reboot qualifier.

==Also see==
~[[Shell Shells]]
~[[Sh]]
~[[Ash]]
~[[AshCommands]]
~[[Bash]]
~[[BashCommands]]

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==Categories==
CategoryCommandLine
CategoryTutorial