====== String Processing ======

{{template>meta:template:pageinfo#tpl
|desc=Document some ways that **Bash** handles strings.}}

===== Replacement =====

^ Command/Syntax                                                                                                     ^ Description                         ^
| <wrap cmd>sed 's/<wrap cmdp>regexp</wrap>/<wrap cmdp>replacement</wrap>/'</wrap>                            | Replace the first matched pattern.  |
| <wrap cmd>sed 's/<wrap cmdp>regexp</wrap>/<wrap cmdp>replacement</wrap>/g'</wrap>                           | Replace all matched patterns.       |
| <wrap cmd>${<wrap cmdp>Variable</wrap>/<wrap cmdp>regexp</wrap>/<wrap cmdp>replacement</wrap>}</wrap>       | Replace the first matched pattern.  |
| <wrap cmd>${<wrap cmdp>Variable</wrap>%%//%%<wrap cmdp>regexp</wrap>/<wrap cmdp>replacement</wrap>}</wrap>  | Replace all matched patterns.       |

===== Deletion =====

^ Command/Syntax                                                                                                     ^ Description                         ^
| <wrap cmd>${<wrap cmdp>Variable</wrap>%<wrap cmdp>pattern</wrap>}</wrap>  | Remove trailing matched pattern.       |
| <wrap cmd>${<wrap cmdp>Variable</wrap>#<wrap cmdp>pattern</wrap>}</wrap>  | Remove  matched pattern from the head.       |

===== Insertion =====
^ Command                                                                                    ^ Description                                                                 ^ Addend                           ^
| <wrap cmd>sed -i %%"%%<wrap cmdp>line-number</wrap>i <wrap cmdp>content</wrap>%%"%%</wrap>  | Insert <wrap cmdp>content</wrap> before line <wrap cmdp>line-number</wrap>  | [[#addend_1|{{mdi>note-text}}]]  |


==== Addend 1 ====
The <wrap cmdp>line-number</wrap> can also use the following special character:
  * ''$'' - The last line.

=== Demo ===
<WRAP box round>
Insert ''new line 0'' before line 2.
<codeprism lang=bash cmdout=2-4,7-10 hl=8>
cat test 
line 1
line 2
line 3
sed -i "2i new line 0" test 
cat test 
line 1
new line 0
line 2
line 3
</codeprism></WRAP>

<WRAP box round>
Insert ''new line 1'' before the last line.
<codeprism lang=bash cmdout=2-4,7-10 hl=9>
cat test
line 1
line 2
line 3
sed -i "\$i new line 1" test
cat test
line 1
line 2
new line 1
line 3
</codeprism></WRAP>

===== Further Reading =====
  * //[[https://linux.die.net/man/1/sed]]//