Bash-Beginners-Guide

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Bash Guide for Beginners cathy ~> grep -c false /etc/passwd 7 cathy ~> grep -i ps ~/.bash* | grep -v history /home/cathy/.bashrc:PS1="\[\033[1;44m\]$USER is in \w\[\033[0m\] " With the first command, user cathy displays the lines from /etc/passwd containing the string root. Then she displays the line numbers containing this search string. With the third command she checks which users are not using bash, but accounts with the nologin shell are not displayed. Then she counts the number of accounts that have /bin/false as the shell. The last command displays the lines from all the files in her home directory starting with ~/.bash, excluding matches containing the string history, so as to exclude matches from ~/.bash_history which might contain the same string, in upper or lower cases. Note that the search is for the string "ps", and not for the command ps. Now let's see what else we can do with grep, using regular expressions. 4.2.2. Grep and regular expressions If you are not on Linux We use GNU grep in these examples, which supports extended regular expressions. GNU grep is the default on Linux systems. If you are working on proprietary systems, check with the -V option which version you are using. GNU grep can be downloaded from http://gnu.org/directory/. 4.2.2.1. Line and word anchors From the previous example, we now exclusively want to display lines starting with the string "root": cathy ~> grep ^root /etc/passwd root:x:0:0:root:/root:/bin/bash If we want to see which accounts have no shell assigned whatsoever, we search for lines ending in ":": cathy ~> grep :$ /etc/passwd news:x:9:13:news:/var/spool/news: To check that PATH is exported in ~/.bashrc, first select "export" lines and then search for lines starting with the string "PATH", so as not to display MANPATH and other possible paths: cathy ~> grep export ~/.bashrc | grep '\
LABEL=/ / ext3 defaults 1 1 If this option is not used, all the lines from the file system table will be displayed. 4.2.2.2. Character classes A bracket expression is a list of characters enclosed by "[" and "]". It matches any single character in that list; if the first character of the list is the caret, "^", then it matches any character NOT in the list. For example, the regular expression "[0123456789]" matches any single digit. Within a bracket expression, a range expression consists of two characters separated by a hyphen. It matches any single character that sorts between the two characters, inclusive, using the locale's collating sequence and character set. For example, in the default C locale, "[a-d]" is equivalent to "[abcd]". Many locales sort characters in dictionary order, and in these locales "[a-d]" is typically not equivalent to "[abcd]"; it might be equivalent to "[aBbCcDd]", for example. To obtain the traditional interpretation of bracket expressions, you can use the C locale by setting the LC_ALL environment variable to the value "C". Finally, certain named classes of characters are predefined within bracket expressions. See the grep man or info pages for more information about these predefined expressions. cathy ~> grep [yf] /etc/group sys:x:3:root,bin,adm tty:x:5: mail:x:12:mail,postfix ftp:x:50: nobody:x:99: floppy:x:19: xfs:x:43: nfsnobody:x:65534: postfix:x:89: In the example, all the lines containing either a "y" or "f" character are displayed. 4.2.2.3. Wildcards Bash Guide for Beginners Use the "." for a single character match. If you want to get a list of all five-character English dictionary words starting with "c" and ending in "h" (handy for solving crosswords): cathy ~> grep '\' /usr/share/dict/words catch clash cloth coach couch cough crash crush If you want to display lines containing the literal dot character, use the -F option to grep. For matching multiple characters, use the asterisk. This example selects all words starting with "c" and ending in "h" from the system's dictionary: cathy ~> grep '\' /usr/share/dict/words caliph cash catch Chapter 4. Regular expressions 59
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Table of Contents Glossary C.......
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Introduction 1. Why this guide? The
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Revision 1.6 2005-03-01 Revised by:
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Bash Guide for Beginners See Chapte
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touch pic-`date +%s`.jpg sleep 300
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DISKFUL=$(df -h $WEBDIR | grep -v F
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;; 2) $FORTUNE startrek ;; 3) $FORT
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[carol@octarine ~/test] ls -a ./ ..
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Chapter 10. More on variables In th
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Bash Guide for Beginners [bob in ~]
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if [ -z $1 ]; then echo "Usage: $0
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10.3.3. Transformations of variable
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Bash Guide for Beginners The opposi
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Chapter 11. Functions In this chapt
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The commands after && are only exec
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zip2 "$TAR" echo "...done." >> "$LO
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Chapter 12. Catching signals In thi
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Bash Guide for Beginners 2. Write a
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Bash Guide for Beginners jobs kill
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if [ $i -eq 5 ] ArrowUp+Enter or !!
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cd Change directory. cdp/cdplay An
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Bash Guide for Beginners gimp grep
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Send and receive mail. man Read man
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Bash Guide for Beginners rsh RPM Pa
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Index A aliases Section 3.5.1 ANSI-
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J Bash Guide for Beginners K kill k
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eadonly Section 10.1.3 regular expr
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