updates for version 1.5

Author: learnbyexample

code_snippets/BRE_ERE_Regular_Expressions.sh

@@ -1,3 +1,5 @@
+## Line Anchors
+
 printf 'spared no one\npar\nspar\ndare' | grep '^pa'
 
 printf 'spared no one\npar\nspar\ndare' | grep 'ar$'
@@ -6,6 +8,8 @@ printf 'spared no one\npar\nspar\ndare' | grep '^par$'
 
 printf 'spared no one\npar\nspar\ndare' | grep -x 'par'
 
+## Word Anchors
+
 cat word_anchors.txt
 
 grep '\bpar' word_anchors.txt
@@ -22,6 +26,8 @@ grep '\Bpar' word_anchors.txt
 
 grep 'par\B' word_anchors.txt
 
+## Alternation
+
 printf 'I like cats\nI like parrots\nI like dogs' | grep 'cat\|dog'
 
 printf 'I like cats\nI like parrots\nI like dogs' | grep -E 'cat|dog'
@@ -36,13 +42,17 @@ grep --color=auto -E '^|pare' word_anchors.txt
 
 grep --color=auto -E 'sub|put|tar|$' word_anchors.txt
 
-printf 'spared PARTY PaReNt' | grep -ioE 'par|pare|spare'
+echo 'car spared spar' | grep -oE 'are|spared'
+
+echo 'car spared spar' | grep -oE 'spared|are'
 
-printf 'spared PARTY PaReNt' | grep -ioE 'spare|pare|par'
+echo 'pool party 2' | grep -oE 'party|par'
 
-printf 'spared PARTY PaReNt' | grep -ioE 'spa|pared'
+echo 'pool party 2' | grep -oE 'par|party'
 
-printf 'spared PARTY PaReNt' | grep -ioE 'pared|spa'
+echo 'pool party 2' | grep -oP 'par|party'
+
+## Grouping
 
 printf 'red\nreform\nread\narrest' | grep -E 'reform|rest'
 
@@ -54,6 +64,8 @@ printf 'sub par\nspare\npart time' | grep -E '\b(par|part)\b'
 
 printf 'sub par\nspare\npart time' | grep -E '\bpar(|t)\b'
 
+## Escaping metacharacters
+
 echo 'a^2 + b^2 - C*3' | grep 'b^2'
 
 echo '$a = $b + $c' | grep '$b'
@@ -64,7 +76,17 @@ echo '$a = $b + $c' | grep -oF '$' | wc -l
 
 printf '(a/b) + c\n3 + (a/b) - c' | grep '^(a/b)'
 
-printf '(a/b) + c\n3 + (a/b) - c' | grep -E '^\(a/b\)'
+printf '(a/b) + c\n3 + (a/b) - c' | grep -E '^\(a/b)'
+
+## Matching characters like tabs
+
+echo 'attempt' | grep -o 'a\tt'
+
+printf 'go\tto\ngo to' | grep $'go\tto'
+
+printf 'go\tto\ngo to' | grep $'go\x20to'
+
+## The dot meta character
 
 echo 'tac tin cot abc:tuv excite' | grep -o 'c.t'
 
@@ -74,6 +96,8 @@ printf '42\t33\n' | grep -o '2.3'
 
 grep -xE 'c..(t|l)y' words.txt
 
+## Quantifiers
+
 printf 'fed\nfod\nfe:d\nfeed' | grep -wE 'fe.?d'
 
 printf 'sub par\nspare\npart time' | grep -wE 'part?'
@@ -108,10 +132,16 @@ echo 'a cat and a dog' | grep -E 'cat.*dog|dog.*cat'
 
 echo 'dog and cat' | grep -E 'cat.*dog|dog.*cat'
 
+## Longest match wins
+
 echo 'foot' | grep -oE 'f.?o'
 
 echo 'car bat cod map scat dot abacus' | grep -o '.*'
 
+echo 'foo123312baz' | grep -oE 'o(1|2|3)+(12baz)?'
+
+echo 'foo123312baz' | grep -oP 'o(1|2|3)+(12baz)?'
+
 echo 'car bat cod map scat dot abacus' | grep -o '.*m'
 
 echo 'car bat cod map scat dot abacus' | grep -o 'c.*t'
@@ -120,6 +150,8 @@ echo 'car bat cod map scat dot abacus' | grep -o 'c.*at'
 
 echo 'car bat cod map scat dot abacus' | grep -o 'b.*m*'
 
+## Character classes
+
 printf 'cute\ncat\ncot\ncoat\ncost\nscuttle' | grep 'c[ou]t'
 
 printf 'meeting\ncute\nboat\nsite\nfoot' | grep -E '[aeo]+t'
@@ -180,6 +212,8 @@ echo 'f*(a^b) - 3*(a+b)/(a-b)' | grep -o 'a[+^]b'
 
 echo '5ba\babc2' | grep -o '[a\b]*'
 
+## Backreferences
+
 grep -xE '([a-z]{3})..\1' words.txt
 
 grep -xE '([a-d]..)\1' words.txt
@@ -188,9 +222,31 @@ echo 'effort flee facade oddball rat tool' | grep -owE '\w*(\w)\1\w*'
 
 printf 'spot the the error\nno issues here' | grep -wE '(\w+)\W+\1'
 
+## Known Bugs
+
 grep -m5 -xiE '([a-z]*([a-z])\2[a-z]*){2}' words.txt
 
 grep -m5 -xiE '[a-z]*([a-z])\1[a-z]*([a-z])\2[a-z]*' words.txt
 
 grep -m5 -xiP '([a-z]*([a-z])\2[a-z]*){2}' words.txt
 
+echo 'cocoa' | grep -E '(\bco){2}'
+
+echo 'cocoa' | grep -E '\bco\bco'
+
+echo 'cocoa' | grep -P '(\bco){2}'
+
+echo 'it line with it here sit too' | grep -oE 'with(.*\bit\b){2}'
+
+echo 'it line with it here sit too' | grep -oE 'with.*\bit\b.*\bit\b'
+
+echo 'it line with it here sit too' | grep -oP 'with(.*\bit\b){2}'
+
+echo 'it line with it here sit too' | grep -oE 'with(.*\<it\>){2}'
+
+echo 'it line with it here it too' | grep -oE 'with(.*\<it\>){2}'
+
+echo 'it line with it here it too sit' | grep -oE 'with(.*\<it\>){2}'
+
+echo 'it line with it here it too sit' | grep -oP 'with(.*\bit\b){2}'
+

code_snippets/Context_matching.sh

@@ -1,23 +1,33 @@
 cat context.txt
 
+## -A
+
 grep -A2 'blue' context.txt
 
 grep -x -A2 'blue' context.txt
 
+## -B
+
 grep -B2 'bread' context.txt
 
 grep -B3 'ruby' context.txt
 
+## -C
+
 grep -C1 'sky' context.txt
 
 grep -A1 -B2 'sky' context.txt
 
 grep -C2 'kotlin' context.txt
 
+## Contiguous matches
+
 grep -n -C1 'flower' context.txt
 
 grep -n -A4 'blue' context.txt
 
+## Customizing separators
+
 seq 29 | grep --group-separator='*****' -A1 '3'
 
 grep -A0 --group-separator='*-----------*-----------*' 'in' context.txt

code_snippets/Frequently_used_options.sh

@@ -1,6 +1,4 @@
-printf '42\n' | file -
-
-printf '42\r\n' | file -
+## Simple string search
 
 cat programming_quotes.txt
 
@@ -10,6 +8,12 @@ grep 'e th' programming_quotes.txt
 
 printf 'avocado\nmango\nguava' | grep 'v'
 
+printf '42\n' | file -
+
+printf '42\r\n' | file -
+
+## Fixed string search
+
 echo 'int a[5]' | grep 'a[5]'
 
 echo 'int a[5]' | grep 'a['
@@ -20,14 +24,20 @@ echo 'int a[5]' | grep -F 'a[5]'
 
 echo 'int a[5]' | fgrep 'a[5]'
 
+## Case insensitive search
+
 grep -i 'jam' programming_quotes.txt
 
 printf 'Cat\ncOnCaT\nscatter\ncut' | grep -i 'cat'
 
+## Invert matching lines
+
 seq 5 | grep -v '3'
 
 printf 'goal\nrate\neat\npit' | grep -v 'at'
 
+## Line number and count
+
 grep -n 'not' programming_quotes.txt
 
 printf 'great\nnumber\numpteen' | grep -n 'r'
@@ -40,10 +50,14 @@ seq 15 | grep -c '1' programming_quotes.txt -
 
 cat <(seq 15) programming_quotes.txt | grep -c '1'
 
+## Limiting output lines
+
 grep -m3 'in' programming_quotes.txt
 
 seq 1000 | grep -m4 '2'
 
+## Multiple search strings
+
 grep -e '1' -e 'two' programming_quotes.txt
 
 printf 'two\n1\n' > search_strings.txt
@@ -56,6 +70,8 @@ grep -f search_strings.txt -e 'twice' programming_quotes.txt
 
 grep 'in' programming_quotes.txt | grep 'not'
 
+## Filename instead of matching lines
+
 grep -l 'are' programming_quotes.txt search_strings.txt
 
 grep -l 'xyz' programming_quotes.txt search_strings.txt
@@ -66,6 +82,8 @@ grep -L 'xyz' programming_quotes.txt search_strings.txt
 
 grep -L 'are' programming_quotes.txt search_strings.txt
 
+## Filename prefix for matching lines
+
 grep '1' programming_quotes.txt
 
 seq 1000 | grep -h -m3 '1' - programming_quotes.txt
@@ -78,6 +96,8 @@ grep -Hn '1' *
 
 vim -q <(grep -Hn '1' *)
 
+## Colored output
+
 grep --color=auto -m3 'in' programming_quotes.txt
 
 grep --color=auto -n -e '1' -e 'worth' *.txt
@@ -90,6 +110,8 @@ alias grep='grep --color=auto'
 
 grep --color=always 'not' programming_quotes.txt | less -R
 
+## Match whole word or line
+
 printf 'par value\nheir apparent\n' | grep 'par'
 
 printf 'par value\nheir apparent\n' | grep -w 'par'
@@ -104,6 +126,8 @@ grep -x '1' *.txt
 
 grep -cx '' programming_quotes.txt
 
+## Comparing lines between files
+
 printf 'teal\nlight blue\nbrown\nyellow\n' > colors_1
 
 printf 'blue\nblack\ndark green\nyellow\n' > colors_2
@@ -114,6 +138,8 @@ grep -Fvxf colors_1 colors_2
 
 grep -Fvxf colors_2 colors_1
 
+## Extract only matching portion
+
 grep -o -e 'twice' -e 'hard' programming_quotes.txt
 
 grep -c 'in' programming_quotes.txt

code_snippets/Gotchas_and_Tricks.sh

@@ -1,3 +1,5 @@
+## Shell quoting
+
 echo 'a cat and a dog' | grep and a
 
 echo 'a cat and a dog' | grep 'and a'
@@ -18,6 +20,8 @@ echo '\S*\Q'"$expr"'\E\S*'
 
 echo 'f*(2-a/b) - 3*(a^b)-42' | grep -oP '\S*\Q'"$expr"'\E\S*'
 
+## Patterns starting with hyphen
+
 printf '-2+3=1\n'
 
 echo '5*3-2=13' | grep '-2'
@@ -32,6 +36,8 @@ printf 'boat\nsite\nfoot' | grep '[aeo]+t'
 
 printf 'boat\nsite\nfoot' | grep '[aeo]+t' -E
 
+## Word boundary differences
+
 echo '*$' | grep '\b\$\b'
 
 echo '*$' | grep -w '\$'
@@ -42,24 +48,40 @@ echo 'I have 12, he has 2!' | grep -o '\<..\>'
 
 echo 'I have 12, he has 2!' | grep -ow '..'
 
-mkdir gotchas_tricks && cd $_
+## Faster execution for ASCII input
+
+time grep -xE '([a-d][r-z]){3}' words.txt > f1
+
+time LC_ALL=C grep -xE '([a-d][r-z]){3}' words.txt > f2
+
+diff -s f1 f2
+
+time grep -xE '([a-z]..)\1' words.txt > f1
+
+time LC_ALL=C grep -xE '([a-z]..)\1' words.txt > f2
+
+rm f[12]
+
+/bin/grep --version | head -n1
 
-wget https://www.gutenberg.org/files/60/60.txt -O scarlet_pimpernel.txt
+time /bin/grep -wE '([a-d][r-z]){3}' words.txt > f1
 
-file scarlet_pimpernel.txt 
+grep --version | head -n1
 
-time grep -wE '([a-d][r-z]){3}' scarlet_pimpernel.txt > f1
+time grep -wE '([a-d][r-z]){3}' words.txt > f2
 
-time LC_ALL=C grep -wE '([a-d][r-z]){3}' scarlet_pimpernel.txt > f2
+rm f[12]
 
-cd ../bre_ere/
+## Speed benefits with PCRE
 
 time LC_ALL=C grep -xE '([a-z]..)\1' words.txt > f1
 
 time LC_ALL=C grep -xP '([a-z]..)\1' words.txt > f2
 
 rm f[12]
 
+## Parallel execution
+
 wget https://github.com/torvalds/linux/archive/v4.19.tar.gz
 
 tar -zxf v4.19.tar.gz
@@ -78,15 +100,5 @@ diff -sq <(sort ../f1) <(sort ../f2)
 
 diff -sq <(sort ../f1) <(sort ../f3)
 
-cd ..
-
-/bin/grep --version | head -n1
-
-time /bin/grep -wE '([a-d][r-z]){3}' scarlet_pimpernel.txt > f1
-
-grep --version | head -n1
-
-time grep -wE '([a-d][r-z]){3}' scarlet_pimpernel.txt > f2
-
-rm f[1-3]
+rm ../f[1-3]