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3.5 KiB
Markdown
154 lines
3.5 KiB
Markdown
# The `cat` command
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---
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The `cat` command allows us to create single or multiple files, to view the content of a file or to concatenate files and redirect the output to the terminal or files.
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The "cat" stands for 'concatenate.' and it's one of the most frequently used commands in the Linux terminal.
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### Examples of uses:
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1. To display the content of a file in terminal:
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```
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cat <specified_file_name>
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```
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2. To display the content of multiple files in terminal:
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```
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cat file1 file2 ...
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```
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3. To create a file with the cat command:
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```
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cat > file_name
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```
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4. To display all files in current directory with the same filetype:
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```
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cat *.<filetype>
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```
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5. To display the content of all the files in current directory:
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```
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cat *
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```
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6. To put the output of a given file into another file:
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```
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cat old_file_name > new_file_name
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```
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7. Use cat command with `more` and `less` options:
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```
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cat filename | more
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cat filename | less
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```
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8. Append the contents of file1 to file2:
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```
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cat file1 >> file2
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```
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9. To concatenate two files together in a new file:
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```
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cat file1_name file2_name merge_file_name
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```
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10. Some implementations of cat, with option -n, it's possible to show line numbers:
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```
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cat -n file1_name file2_name > new_numbered_file_name
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```
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### Syntax:
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```
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cat [OPTION] [FILE]...
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```
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### Additional Flags and their Functionalities:
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|**Short Flag** |**Long Flag** |**Description** |
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|:---|:---|:---|
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|`-A`| `--show-all` |equivalent to -vET|
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|`-b`| `--number-nonblank` |number nonempty output lines, overrides -n|
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|`-e`|<center>-</center>| equivalent to -vE|
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|`-T`|<center>-</center>|Display tab separated lines in file opened with ```cat``` command.|
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|`-E`|<center>-</center>|To show $ at the end of each file.|
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|`-E`|<center>-</center>|Display file with line numbers.|
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|`-n`| `--number`|number all output lines|
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|`-s`| `--squeeze-blank`|suppress repeated empty output lines|
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|`-u`|<center>-</center>|(ignored)|
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|`-v`| `--show-nonprinting`|use ^ and M- notation, except for LFD and TAB|
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|<center>-</center>|`--help` |display this help and exit|
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|<center>-</center>|`--version`|output version information and exit|
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---
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# The `tac` command
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`tac` is a Linux command that allows you to view files line-by-line, beginning from the last line. (tac doesn't reverse the contents of each individual line, only the order in which the lines are presented.) It is named by analogy with `cat`.
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### Examples of uses:
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1. To display the content of a file in terminal:
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```
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tac <specified_file_name>
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```
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2. This option attaches the separator before instead of after.
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```
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tac -b concat_file_name tac_example_file_name
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```
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3. This option will interpret the separator as a regular expression.
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```
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tac -r concat_file_name tac_example_file_name
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```
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4. This option uses STRING as the separator instead of newline.
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```
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tac -s concat_file_name tac_example_file_name
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```
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5. This option will display the help text and exit.
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```
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tac --help
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```
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6. This option will give the version information and exit.
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```
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tac --version
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```
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### Syntax:
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```
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tac [OPTION]... [FILE]...
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```
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### Additional Flags and their Functionalities:
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|**Short Flag** |**Long Flag** |**Description** |
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|:---|:---|:---|
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|`-b`|`--before`|attach the separator before instead of after|
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|`-r`| `--regex`|interpret the separator as a regular expression|
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|`-s`| `--separator=STRING`|use STRING as the separator instead of newline|
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|<center>-</center>|`--help`|display this help and exit|
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|<center>-</center>|`--version`|output version information and exit|
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