tar
PART 01
Function Description: Add or restore files from backup files
Syntax: tar -f[cxzjv] <file>
Parameters: -f is a required parameter
-c Create a backup file
-x Extract files from the backup file
-z Use gzip/gunzip to compress/decompress files
-j Use bzip2/bunzip2 to compress/decompress files
-v Show the command execution process
Example: tar -cf newfile.tar file1 file2 packages file1 and file2 into newfile.tar
tar -xf newfile.tar extracts files from newfile.tar
tar -czvf newfile.tar.gz file1 file2 packages file1 and file2 and uses gzip to compress the files into newfile.tar.gz
tar -xzvf newfile.tar.gz decompresses newfile.tar.gz and extracts the files inside
zip
PART 02
Function Description: Compress and generate files ending with “.zip”
Syntax: zip [-1..9][-r] <newfile.zip> <sourcefile/dir>
Parameters: -r processes all files and directories in subdirectories
-1..9 compression efficiency, the larger the number, the higher the compression efficiency
Example: zip newfile.zip file1 file2 compresses file1 and file2 into newfile.zip
Decompression method: use unzip to decompress, unzip newfile.zip
gzip
PART 03
Function Description: Compress and generate files ending with “.gz”
Syntax: gzip [-1..9][-r] <file/dirname>
Parameters: -r compresses files in the directory but does not compress the directory itself
-1..9 compression efficiency, the larger the number, the higher the compression efficiency (default 6)
Example: gzip file compresses file into file.gz and deletes the source file
Decompression method: use gunzip to decompress, gunzip file.gz
bzip2
PART 04
Function Description: Compress and generate files ending with “.bz2”
Syntax: bzip2 <file>
Example: bzip2 file compresses file into file.bz2 and deletes the source file
Decompression method: use bunzip2 to decompress, bunzip2 file.bz2
sort
PART 05
Function Description: Sort the contents of a text file
Syntax: sort [-nkr] <filename>
Parameters: -n/-g sorts the file by numerical size from smallest to largest (default sorts by ASCII code from smallest to largest)
-k <num> sorts the file by the content of the num-th column (default is the first column)
-r reverse sorting
Example: sort file sorts the file by the ASCII code value of the first column from smallest to largest and outputs.
sort -n -k 3 file sorts the file by the numerical size of the 3rd column from smallest to largest.
sort -nr -k1,2 file sorts the file in reverse order by numerical size, prioritizing the first column, then the second column
uniq
PART 06
Function Description: Merge adjacent identical lines in a file
Syntax: uniq [-cd] <file> [outfile]
Parameters: -c displays the count of repetitions for each line in the first column
-d only displays lines that have duplicates
Example: uniq -c file merges identical lines and counts the number of repetitions for each line, outputting to the screen
uniq -d file outfile merges identical lines and displays lines that appear multiple times in the file, outputting to outfile
wc
PART 07
Function Description: Count the number of bytes in a file
Syntax: wc [-cwl] <file>
Parameters: -c counts only the number of bytes
-w counts only the number of words
-l counts only the number of lines
Example: wc file displays the number of bytes, words, and lines in the file
wc -l file displays the number of lines in the file
grep
PART 08
Function Description: Find lines in a file that match a condition
Syntax: grep [-v] <string> <file>
Parameters: -v does not match, displays lines in the file that do not match the string
Example: grep world file finds lines in the file that contain “world”
grep -v world file finds lines in the file that do not contain “world”
awk
PART 09
Function Description: Perform operations on specific columns of specific lines
Syntax: awk [-F] ‘(condition){operate}’ <filename>
Parameters: -F specifies the delimiter for columns, which can be any character, default is whitespace
Example: awk -F “:” ‘{print $1}’ splits by “:” and prints the first column
awk ‘($1 > 100){print $0}’ outputs the entire line for rows where the first column is greater than 100
awk ‘($1 > 100){print $1 “\t” $2}’ outputs the first and second columns for rows where the first column is greater than 100, separated by “\t”.
awk ‘($3~/world/){ x+= $1} END{print x}’ sums the first column for rows where the third column matches “world”, and outputs the result x after processing is complete
sed
PART 10
Function Description: Text processing and editing of files
Syntax: sed [-i] ‘{command}’ <filename>
Parameters: -i modifies the original file directly (default modifies and outputs to screen, original file remains unchanged)
Example: sed -i ‘s/test/new_word/’ file replaces the string “test” in the file with “new_word”
sed -i ‘/pattern/ s/ test/new_word/’ file performs replacement on lines in the file that match the pattern string
sed -i ‘/^$/ d’ file deletes empty lines from the file
md5sum
PART 11
Function Description: Verify the integrity of file transfers
Syntax: md5sum [-c] <filename>
Parameters: -c checks whether the file transfer is complete
Example: md5sum file1 generates the md5 value for file1.
md5sum file1 > newfile generates the md5 value for file1 and redirects it to newfile.
md5sum -c newfile checks whether the md5 value in newfile matches the file.
chmod
PART 12
Function Description: Set file or directory permissions
Syntax: chmod [-R] <mode> <file/dirname>
Parameters: -R sets permissions for the directory and all files within it
Detailed Description: File permissions are divided into whether they are readable (r), writable (w), and executable (x), corresponding to the owner (u), group members (g), and others (o). Mode can be in symbolic or numeric form.
Symbolic mode: [ugoa] [+-=] [rwx]
Numeric mode: represented by 1/0, where 111 means readable, writable, and executable, and 000 means not readable, not writable, and not executable. Readable, writable, and executable correspond to decimal 4, 2, and 1, so 5 means readable, not writable, and not executable.
Example: chmod u+xg=rx o-rwx file adds executable permission for the user of the file, sets group member permissions to readable and writable, and removes rwx permissions for others.
chmod -R 750 dirname sets permissions for the dirname directory and all files within it to be readable, writable, and executable for the user, readable and executable for group members, and no permissions for others.
find
PART 13
Function Description: Find files
Syntax: find [path] [expression]
Detailed Description: path searches under the specified path
expression search pattern, commonly used include
-name <filename> search by filename (wildcards allowed)
-perm <mode> search by file permissions
-user <user name> search by file owner
-group <group name> search by file group
-mtime <+n/-n> search by file modification time, -n means modified within n days, +n means modified more than n days ago
-type <l/d/f> search by file type, l: symbolic link, f: regular file, d: directory
Example: find ./ -name file searches for files named “file” in the current directory and its subdirectories
find ./ -name ‘*a’ -type d finds directory files whose names end with “a”.
du
PART 14
Function Description: Display the size of directories or files
Syntax: du [-ash] [–max-depth=<n>] <file/dirname>
Parameters: -a displays the size of individual files in the directory
-s displays only the total
-h displays in units of “K”, “M”, “G”
–max-depth=<n> displays files within n levels of directories only
Example: du -sh ./ displays the size of the current directory
du -ah –max-depth=1 dir displays the sizes of all files in the dir directory, excluding the next level of directories
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