Commands Continued..

View file content

cat file1	view the contents of a file starting from the first row
tac file1	view the contents of a file starting from the last line
more file1	view content of a file along
less file1	similar to 'more' command but which allows backward movement in the file as well as forward movement
head -2 file1	view first two lines of a file
tail -2 file1	view last two lines of a file
tail -f /var/log/messages	view in real time what is added to a file

Text Manipulation

cat file1 file2 ... | command <> file1_in.txt_or_file1_out.txt	general syntax for text manipulation using PIPE, STDIN and STDOUT
cat file1 | command( sed, grep, awk, grep, etc...) > result.txt	general syntax to manipulate a text of a file, and write result to a new file
cat file1 | command( sed, grep, awk, grep, etc...) >> result.txt	general syntax to manipulate a text of a file and append result in existing file
grep Aug /var/log/messages	look up words "Aug" on file '/var/log/messages'
grep ^Aug /var/log/messages	look up words that begin with "Aug" on file '/var/log/messages'
grep [0-9] /var/log/messages	select from file '/var/log/messages' all lines that contain numbers
grep Aug -R /var/log/*	search string "Aug" at directory '/var/log' and below
sed 's/stringa1/stringa2/g' example.txt	replace "string1" with "string2" in example.txt
sed '/^$/d' example.txt	remove all blank lines from example.txt
sed '/ *#/d; /^$/d' example.txt	remove comments and blank lines from example.txt
echo 'esempio' | tr '[:lower:]' '[:upper:]'	convert from lower case in upper case
sed -e '1d' result.txt	eliminates the first line from file example.txt
sed -n '/stringa1/p'	view only lines that contain the word "string1"
sed -e 's/ *$//' example.txt	remove empty characters at the end of each row
sed -e 's/stringa1//g' example.txt	remove only the word "string1" from text and leave intact all
sed -n '1,5p;5q' example.txt	view from 1th to 5th row
sed -n '5p;5q' example.txt	view row number 5
sed -e 's/00*/0/g' example.txt	replace more zeros with a single zero
cat -n file1	number row of a file
cat example.txt | awk 'NR%2==1'	remove all even lines from example.txt
echo a b c | awk '{print $1}'	view the first column of a line
echo a b c | awk '{print $1,$3}'	view the first and third column of a line
paste file1 file2	merging contents of two files for columns
paste -d '+' file1 file2	merging contents of two files for columns with '+' delimiter on the center
sort file1 file2	sort contents of two files
sort file1 file2 | uniq	sort contents of two files omitting lines repeated
sort file1 file2 | uniq -u	sort contents of two files by viewing only unique line
sort file1 file2 | uniq -d	sort contents of two files by viewing only duplicate line
comm -1 file1 file2	compare contents of two files by deleting only unique lines from 'file1'
comm -2 file1 file2	compare contents of two files by deleting only unique lines from 'file2'
comm -3 file1 file2	compare contents of two files by deleting only the lines that appear on both files