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42 lines
2.3 KiB
42 lines
2.3 KiB
2 years ago
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#!/bin/sh
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# To make this script executable, use the command: chmod +x 08_regex.sh
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# To run the script, use the command: ./08_regex.sh
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echo "This spell will teach you the basics of regular expressions and pattern matching in POSIX-compliant Bash"
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echo "To study the code of the examples, please use the command: cat 08_regex.sh"
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# Basic regular expressions (special characters)
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echo "Regular expressions are a way to search for patterns in text. Common special characters include:"
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echo "^ - beginning of a line"
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echo "$ - end of a line"
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echo "* - any number of characters"
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echo "? - any single character"
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echo "[] - any character in the brackets"
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echo "() - group characters together"
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echo "| - or"
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echo "\\ - escape special characters"
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# grep (search in text)
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echo "The grep command searches for a pattern in a file or input."
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echo "grep '^root:' /etc/passwd - searches for the pattern '^root:' in the file /etc/passwd"
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echo "Example: grep 'bash' /etc/passwd - searches for the pattern 'bash' in the file /etc/passwd"
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grep 'bash' /etc/passwd
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# sed (replace in text)
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echo "The sed command is a stream editor that can perform basic text transformations on an input stream (a file or input from a pipeline)."
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echo "sed 's/root/admin/' /etc/passwd - replaces the first occurence of 'root' with 'admin' in the file /etc/passwd"
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echo "Example: sed 's/bash/zsh/' /etc/passwd - replaces the first occurence of 'bash' with 'zsh' in the file /etc/passwd"
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echo "backup" | sed 's/backup/backup_file/'
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# awk (advanced text processing)
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echo "The awk command is a text processing tool that can perform more complex text transformations."
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echo "awk -F: '{ print $1 }' /etc/passwd - prints the first field of each line of the file /etc/passwd, where the field separator is ':'"
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awk '{ print $1 }' /etc/passwd
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echo "root:x:0:0:root:/root:/bin/bash" | awk -F: '{print $1}'
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# find and xargs (run command for all found files)
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echo "The find command is used to search for files in a directory hierarchy. xargs is used to build and execute command lines from standard input."
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echo "find / -name '*.txt' | xargs grep 'example' - searches for all .txt files in the root directory and its subdirectories, and runs 'grep 'example'' on each file found"
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find /etc -name "*.conf" -exec grep "root" {} \;
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echo "Spell cast successfully"
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