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start=$(date +%s) 
sleep 5
end=$(date +%s)
echo "The process lasted $(expr $end - $start) seconds." 

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cat -n afile >result && rm afile # rm will be executed only if cat succeds

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touch afile 
copy afile bfile || echo Copy failed # the echo will be executed

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showtime() 
{
   local TZIN=$1
   local TZOUT=$2
   local TIME=$3
   echo -n "$TZIN $TZOUT $TIME"
   TZ=$TZOUT date --date="TZ=\"$TZIN\" $TIME"
}

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for i in Europe/London Europe/Paris Europe/Madrid; do
    showtime America/Los_Angeles $i 11:45
done

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TZONES='America/Los_Angeles America/New_York Europe/London'
for tzin in $TZONES; do
    for tzout in $TZONES; do
      showtime $$tzin $tzout 11:45
    done
done

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ls | 
while read name ; do # For every entry
    if [ -f $name -a -r $name ] ; then # If is a regular file and readable
      echo -n "$name "
      expr $(wc -c <$name) / $(wc -l <$name)#display average characters per line
    fi
done |
head

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touch sourcefile
touch destfile

# Make source newer than destination
if test [ soutcefile -nt destfile ] ; then
    cp sourcefile destfile
    echo Refreshed destfile
fi

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if test [ soutcefile -nt destfile] ; then
   cp sourcefile destfile
   echo Refreshed destfile
else
   echo destfile is up to date
fi

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find . -type f | # Output the name of all files
xargs cat | # Combining them by applying cat
wc -l # Count number of lines

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case $(uname) in Linux

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git clone gitrepo; cd gitrepo
git log --pretty=format:%aD master | # Fetch commit dates
cut -d, -f1 # Select the weekday
sort |      # Bring all weekdays together
uniq -c |   # Count all weekday occurrences
sort -rn     # Order by descending popularity

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echo $(date): operation failed >>log-file

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curl -s "http://api.currencylayer.com/\                                     Thursday 26 March 07:04
live?access_key=$API_KEY&source=USD&currencies=EUR" | jq .

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echo "SELECT COUNT(*) FROM projects" | # SQL query
mysql -ughtorrent -p ghtorrent # MySQL client and database

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echo 'select url from projects limit 3' | # Obtain URL of first three projects
mysql -ughtorrent -p ughtorrent | # Invoke MySQL client
while read url ; do
    curl -s $url | # Fetch project's details
    jq -r '{owner: .owner.login, name: .name, pushed: .pushed_at}' # Print owner, project, and last push time
done

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curl -Ls https://github.com/castor-software/depclean/archive/1.0.0.tar.gz | # Download tar file
tar -tzvf - | # -t list content, z- indicates zip compression, -v is verbose, -f retrieve file to the output of curl 
head -10 # list first 10 entries

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curl -Ls https://github.com/castor-software/depclean/archive/1.0.0.tar.gz | # Download tar file
tar -xzf - 

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tar -czf share.tar.gz /usr/share

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mkdir dict2
(
    cd /usr/share/dict
    tar -cf - .
) | (
    cd dict2
    tar -xf -
)
ls dict2

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ls -lR /home/joe >ls.out ; gzip ls.out

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git log --pretty=format:%ae | # list each commit author email                                            Saturday  4 April 10:24 148 ↵
sort | # Bring emails together
uniq -c | # Count occurrence
sort -rn | # Order by number
head 

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find . -type f -print |                                                         
    while read f ; do # For each file
    echo -n "$f " # Prints its name on a single line
    git log --follow --oneline $f | wc -l # Count the number of changes
    done |
    sort -k 2nr | # Sort by the second field in reverse numerical order
    head

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git blame --line-porcelain src/main/java/spoon/Launcher.java | # obtain line metadata
head -15

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git blame --line-porcelain src/main/java/spoon/Launcher.java |
grep "^author " | #Show each line's author
sort |  # Order by author
uniq -c | # Count author instances
sort -rn | # Order by count
head

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date +%s # show date in epoch
date -d @1585990273 # parse data from epoch to date

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date -d @$(
   git blame --line-porcelain src/main/java/spoon/Launcher.java |
   awk "/^author-time / {sum += $2; count++} # Maintain sum and count of commit times
   END {printf("%d", sum / count)}"
)

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file=src/main/java/spoon/Launcher.java # File to examine
git log --pretty=format:%H -3 $ $file # Show SHA of commmits
git log --pretty=format:%H $file | # Obtain commits' SHA
while read sha ; do # For each SHA
    git show $sha:$file | # List files stated at that commit
    wc -l
done |
head -15 # First 15 entries

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for i in $(seq 50) ; do
    echo -n "." # displais 50 dots
done

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cd /usr/share/dict
grep baba words # All lines (words) containing baba
grep "^baba" words # All lines (words) starting with baba
grep "baba$" words # All lines (words) ending with baba
grep a.a.a.a words # Words containing a followed by anything

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grep "^t.y$" words # Three letter words starting with t, ending with y
grep "^....$" words | wc -l # Number of four letter words
grep "^k.*d.*k$" words # Words starting with k, ending with k, and with a d in between
grep "^a*b*c*d*e*f*g*h*i*j*k*l*m*n*o*p*q*r*s*t*u*v*w*x*y*z*$" words | wc -l # words that follow the alphabetical order
grep "[0-9]" words # Lines containing a digit
grep "^k.[bdgkpt].k$" words # Words with a hard consonant between ks
grep "^[A-Z]" words | wc -l # Number of proper nouns
grep "[^A-Za-z]" words # Lines with non-alphabetic characters
find ~/Downloads | grep "[[:space:]]" # List files with space characters

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grep -E "s{2}" words  # Words with two secuentical s characters
grep -E "[^aeiouy]{7}" words # Words with seven consonants
grep -E "^.{,15}$" words | wc -l # Words with a length up to 15
grep -E "^.{15,}$" words | wc -l # Words with at least 15 characters
grep -E "^(.).*\1$" words | head # Words beginning and ending with the same character (the character in parentesis is referenced with \1)
grep -E "^(.)(.)((.)\4)?\2\1$" words # Find 3-4 letter palindromes 

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grep -E "^(aba|ono).*(ly|ne)$" words # Words with alternative start/end parts
grep -l vfs *.c # List C files containing vfs

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grep -rl read_iter . | head -5 # Search recursively all the files that contain the string read_iter

grep -F ... *.c | head

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cd /etc/passwd
cut -d: -f 1 /etc/passwd | head -4 # Output the first field

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awk "/bash/" /etc/passwd # Output lines containing "bash"
awk -F: "$3 > 1000" /etc/passwd # Lines where field 3 > 1000
awk -F: "{print $1}" /etc/passw | head -5 # Output field 1
awk "!/^#/ {print $1}" /etc/services | head # Print first field that doesn't match the regular expression

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ack --ruby foo # Find foo in occurrences in ruby files
ack abc -l # List files with the occurrence of abc character

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sort -k 2 dates | head -5 # Sort by second and subsequent fields (space separated)
sort -k 4r dattes | head # Sorts in reverse order
sort -k 3M -k 2n dates | head  # sort 3rd field (Month) in chronological order, then second field (Month day) in numberical order

sort -t : -k 4n /etc/passwd | head # Sort by numeric group-id

sort -u /etc/passw | head # sort the unique elements
sort dates | sort -C && echo "Sorted"

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comm linux.bin freebsd.bin

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vim tojson.sed

#!/bin/bash
li``
[ # Insert [ at the beginning
s/.*/ "&",/ # Convert lines into strings
$a\  # Append ] at the end
]
EOF

ls /usr | tojson.sed

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ll > contents.txt 
awk '                    
{ size += $5; n++ }  # Sum size and number of files
END {                # Print summary
print "Total size " size
print "Number of files " n
print "Average file size " size/n
}
' contents.txt

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ll > contents.txt 
awk '
{
sub(".*/", "", $9)   # Remove path
if (!sub(".*\\.", "", $9))    # Keep only extension
next     # Skip files without extension
size[$9] += $5    # Tally size of extension
}
END {
for (i in size)
print i, size[i]
}' content.txt |
sort -k 2nr |
head

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diff -u a b

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patch john.c <mary.patch # Patch John's copy with Mary's patch

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test -d / && echo Directory # Test if root is a directory
test -f / && echo File # Test if root is a file
test hi = there && echo Same # Test if strings are equal
test hi != hi && echo Different # Test if strings are different
test -z "" && echo Empty # Test if string is empty
test -n "a string" && echo Non-empty # Test if string is non empty
test 32 -eq 42 && echo Equal # Test integers are equal
test 32 -lt 50 && echo Less than # Test if integer less than other
test . -nt / && echo . is newer than / # Test if a file is newer than other
test -w / && echo Writable # Test if a file is writable

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expr 1 + 2
expr 2 \* 10
expr 12 \% 5
expr 10 \< 50
expr 5 = 12 # Test of equality
expr John \> Mary # Compare strings
expr \(1 + 20 \) \* 2
expr length "To be or not to be" # String length
expr substr "To be or not to vbe" 4 2 # Substring of 2 from 4
expr "" \| b # Short-circuit OR (first part failed)

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i=0
while [ $i -lt 10 ]; do
    echo $i
    i=$((i + 1))
done

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echo 'This is a test' | tr ' ' - # Replace space with -
echo 'This is a test' | tr a-z A-Z # Replace a-z A-Z

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openssl enc -e -aes-256-cbc -pbkdf2 <pride-and-prejudice.txt >real-secret
freq real-secret
$ openssl enc -d -aes-256-cbc -pbkdf2 <real-secret | head

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ll | tac

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tail /usr/share/dict/words | rev # Reverse characters

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paste - /usr/share/dict/word

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shuf -n 5 /usr/share/dict/words # Output five random words
shuf -n 1 -e heads tails # Throw a single coin

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split -l 10000 -d /usr/share/dict/words # Split the dictionary

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head /etc/passwd | rs -c: -C: -T # Transposes the output

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cho "digraph talks {
        bob [gender="male"];
        eliza [gender="female"];
        fred [gender="male"];
        john [gender="male"];
        mary [gender="female"];
        steve [gender="male"];
        sue [gender="female"];
        mark [gender="male"];

        john -> mary;
        john -> bob;
        mary -> sue;
        sue -> bob;
        sue -> mary;
        fred -> bob;
        eliza -> steve;
}" > talk.dot

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gvpr 'N {clone($0, $)}' talk.dot # Clone each node to the output graph
gvpr

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tifftopnm image.tiff | pnmtopng >image.png # Convert from TIFF to PNG

for i in *.tiff ; do # For each TIFF file
> pngname=$(basename $i .tiff).png # Compute name of PNG file
> tifftopnm $i | # Convert image to PNM
> pnmtopng >$pngname # Convert and write to PNG file
> done

tifftopnm image.tiff | # Convert TIFF to PNM
> pamscale -width=1024 | # Scale to 1024 pixels
> pnmtopng >image.png # Write the result in PNG format

jpegtopnm plate.jpeg |
> pamflip -r90 | # Rotate the image by 90 degrees
> pamscale -width=1024 | # Scale to 1024 pixels
> pnmtojpeg >rplate.jpeg # Write the result in JPEG format

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play -q sox-orig.wav

sox sox-orig.wav sox-orig.mp3 # Convert between file formats
sox sox-orig.wav sox-low.wav pitch -600 # Lower pitch by 600 cents
play -q sox-low.wav

sox sox-orig.wav sox-fast.wav tempo 1.5 # Increase tempo by 50%
play -q sox-fast.wav

sox sox-orig.wav sox-chorus.wav chorus 0.5 0.9 50 0.4 0.25 2 -t \
60 0.32 0.4 2.3 -t 40 0.3 0.3 1.3 -s # Apply chorus effect
play -q sox-chorus.wav

wget -q -O persephone.mp3 \
http://ccmixter.org/content/hansatom/hansatom_-_Persephone.mp3 # By Hans Atom (CC BY 2.5)
sox persephone.mp3 persephone-trimmed.mp3 fade 0 0:06 1 # Trim to 6s with 1s fade-out
play -q persephone-trimmed.mp3

sox --combine mix -v 0.2 persephone-trimmed.mp3 sox-orig.wav \
sox-persephone.mp3 # Mix the two audio files
play -q sox-persephone.mp3

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echo Error >&2 # Send output to standard error

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cat >tmpdir.sh <<\EOF
#!/bin/sh
TMPDIR="${TMP:-/tmp}/$$" # Create temporary directory name
trap 'rm -rf "$TMPDIR"' 0 # Remove it when exiting
trap 'exit 2' 1 2 15 # Exit when the program is interrupted
mkdir "$TMPDIR" # Create the directory
# Do some work in $TMPDIR
EOF

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command <file # A redirection is all that's needed

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if ! command ; then # A simple negation will do
   echo Error >&2
fi

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grep -r pattern . # Modern recursive search

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for i in * ; do # can be replaced by a wildcard
   . . .
done

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cut -d : -f 1,7 # More efficient way to print fields 1 and 7
expr "$LANG" : '.*\.\(.*\)' # More efficient way to isolate encoding
UTF-8

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echo $LANG
en_US.UTF-8