BashFAQ Mirror

This is an unofficial emergency mirror of the great BashFAQ at Greg's wiki. In case Greg's wiki is down, these pages will keep up the information for you ;)

Also it might be useful for regular searches, since Greg's private internet connection is usually under high load and sometimes slow.

• FAQ001 How can I read a file (data stream, variable) line-by-line?
• FAQ002 How can I store the return value/output of a command in a variable?
• FAQ003 How can I insert a blank character after each character?
• FAQ004 How can I check whether a directory is empty or not? How do I check for any *.mpg files?
• FAQ005 How can I use array variables?
• FAQ006 How can I use variable variables (indirect variables, pointers, references) or associative arrays?
• FAQ007 Is there a function to return the length of a string?
• FAQ008 How can I recursively search all files for a string?
• FAQ009 My command line produces no output: tail -f logfile | grep 'foo bar'
• FAQ010 How can I recreate a directory hierarchy structure, without the files?
• FAQ011 How can I print the n'th line of a file?
• FAQ012 How do I invoke a shell command from a non-shell application?
• FAQ013 How can I concatenate two variables? How do I append a string to a variable?
• FAQ014 How can I redirect the output of multiple commands at once?
• FAQ015 How can I run a command on all files with the extension .gz?
• FAQ016 How can I use a logical AND/OR/NOT in a shell pattern (glob)?
• FAQ017 How can I group expressions, e.g. (A AND B) OR C?
• FAQ018 How can I use numbers with leading zeros in a loop, e.g. 01, 02?
• FAQ019 How can I split a file into line ranges, e.g. lines 1-10, 11-20, 21-30?
• FAQ020 How can I find and deal with file names containing newlines, spaces or both?
• FAQ021 How can I replace a string with another string in all files?
• FAQ022 How can I calculate with floating point numbers instead of just integers?
• FAQ023 I want to launch an interactive shell that has a special set of aliases and functions, not the ones in the user's ~/.bashrc.
• FAQ024 I set variables in a loop. Why do they suddenly disappear after the loop terminates? Or, why can't I pipe data to read?
• FAQ025 How can I access positional parameters after $9?
• FAQ026 How can I randomize (shuffle) the order of lines in a file? (Or select a random line from a file, or select a random file from a directory.)
• FAQ027 How can two unrelated processes communicate?
• FAQ028 How do I determine the location of my script? I want to read some config files from the same place.
• FAQ029 How can I display the target of a symbolic link?
• FAQ030 How can I rename all my *.foo files to *.bar, or convert spaces to underscores, or convert upper-case file names to lower case?
• FAQ031 What is the difference between test, [ and [[ ?
• FAQ032 How can I redirect the output of 'time' to a variable or file?
• FAQ033 How can I find a process ID for a process given its name?
• FAQ034 Can I do a spinner in Bash?
• FAQ035 How can I handle command-line arguments to my script easily?
• FAQ036 How can I get all lines that are: in both of two files (set intersection) or in only one of two files (set subtraction).
• FAQ037 How can I print text in various colors?
• FAQ038 How do Unix file permissions work?
• FAQ039 What are all the dot-files that bash reads?
• FAQ040 How do I use dialog to get input from the user?
• FAQ041 How do I determine whether a variable contains a substring?
• FAQ042 How can I find out if a process is still running?
• FAQ043 Why does my crontab job fail? 0 0 * * * some command > /var/log/mylog.`date +%Y%m%d`
• FAQ044 How do I create a progress bar?
• FAQ045 How can I ensure that only one instance of a script is running at a time (mutual exclusion)?
• FAQ046 I want to check to see whether a word is in a list (or an element is a member of a set).
• FAQ047 How can I redirect stderr to a pipe?
• FAQ048 Eval command and security issues
• FAQ049 How can I view periodic updates/appends to a file? (ex: growing log file)
• FAQ050 I'm trying to put a command in a variable, but the complex cases always fail!
• FAQ051 I want history-search just like in tcsh. How can I bind it to the up and down keys?
• FAQ052 How do I convert a file from DOS format to UNIX format (remove CRs from CR-LF line terminators)?
• FAQ053 I have a fancy prompt with colors, and now bash doesn't seem to know how wide my terminal is. Lines wrap around incorrectly.
• FAQ054 How can I tell whether a variable contains a valid number?
• FAQ055 Tell me all about 2>&1 -- what's the difference between 2>&1 >foo and >foo 2>&1, and when do I use which?
• FAQ056 How can I untar or unzip multiple tarballs at once?
• FAQ057 How can group entries (in a file by common prefixes)?
• FAQ058 Can bash handle binary data?
• FAQ059 I saw this command somewhere: :(){ :|:& } (fork bomb). How does it work?
• FAQ060 I'm trying to write a script that will change directory (or set a variable), but after the script finishes, I'm back where I started (or my variable isn't set)!
• FAQ061 Is there a list of which features were added to specific releases (versions) of Bash?
• FAQ062 How do I create a temporary file in a secure manner?
• FAQ063 My ssh client hangs when I try to run a remote background job!
• FAQ064 Why is it so hard to get an answer to the question that I asked in #bash?
• FAQ065 Is there a "PAUSE" command in bash like there is in MSDOS batch scripts? To prompt the user to press any key to continue?
• FAQ066 I want to check if [[ $var == foo | $var == bar | $var == more ]] without repeating $var n times.
• FAQ067 How can I trim leading/trailing white space from one of my variables?
• FAQ068 How do I run a command, and have it abort (timeout) after N seconds?
• FAQ069 I want to automate an ssh (or scp, or sftp) connection, but I don't know how to send the password....
• FAQ070 How do I convert Unix (epoch) timestamps to human-readable values?
• FAQ071 How do I convert an ASCII character to its decimal (or hexadecimal) value and back?
• FAQ072 How can I ensure my environment is configured for cron, batch, and at jobs?
• FAQ073 How can I use parameter expansion? How can I get substrings? How can I get a file without its extension, or get just a file's extension?
• FAQ074 How do I get the effects of those nifty Bash Parameter Expansions in older shells?
• FAQ075 How do I use 'find'? I can't understand the man page at all!
• FAQ076 How do I get the sum of all the numbers in a column?
• FAQ077 How do I log history or "secure" bash against history removal?
• FAQ078 I want to set a user's password using the Unix passwd command, but how do I script that? It doesn't read standard input!
• FAQ079 How can I grep for lines containing foo AND bar, foo OR bar? Or for files containing foo AND bar, possibly on separate lines?
• FAQ080 How can I make an alias that takes an argument?
• FAQ081 How can I determine whether a command exists anywhere in my PATH?
• FAQ082 Why is $(...) preferred over `...` (backticks)?
• FAQ083 How do I determine whether a variable is already defined? Or a function?
• FAQ084 How do I return a string (or large number, or negative number) from a function? "return" only lets me give a number from 0 to 255.
• FAQ085 How to write several times to a fifo without having to reopen it?
• FAQ086 How to ignore aliases or functions when running a command?
• FAQ087 How can I get the permissions of a file without parsing ls -l output?
• FAQ088 How can I avoid losing any history lines?
• FAQ089 I'm using a loop which runs once per line of input but it only seems to run once; everything after the first line is ignored?
• FAQ090 How do I prepend a text to a file (the opposite of >>)?
• FAQ091 I'm trying to get the number of columns or lines of my terminal but the variables COLUMNS / LINES are always empty
• FAQ092 How do I write a CGI script that accepts parameters?
• FAQ093 How can I see a progress bar when copying/moving files?
• FAQ094 I want to get an alert when my disk is full (parsing df output).
• FAQ095 I'm getting "Argument list too long". How can I process a large list in chunks?
• FAQ096 ssh eats my word boundaries! I can't do ssh remotehost make CFLAGS="-g -O"!
• FAQ097 How do I determine whether a symlink is dangling (broken)?
• FAQ098 How to add localization support to your bash scripts
• FAQ099 How can I get the newest (or oldest) file from a directory?
• FAQ100 How do I do string manipulations in bash?