Sed&&awk Study notes (1)

Basic use of sed and awk

In sed and awk, each directive consists of two parts: patterns and procedures. A pattern is a regular expression separated by a slash (/). The process formulates one or more actions that will be performed.

During execution, the first instruction in the script is read and the pattern of the current line is detected, and if there is no match, the process is ignored and the next instruction is read. Reads all instructions instead of reading the first instruction that matches the input line.

After all instructions are interpreted and applied to a single row, sed outputs the line and loops through each input row. awk does not automatically output lines, and the instructions in the script control what awk ultimately does.

Using SED

There are two ways to invoke sed: Specify edit instructions on the command line, or put them in a file and provide the name of the file.

Sed-e ' instruction ' file

[email protected] sedawk]# Cat list

John Daggett, 341 King Road, Plymouth MA

Alice Ford, East Broadway, Richmond VA

Orville Thomas, 11345 Oak Bridge Road, Tulsa OK

Terry Kalkas, 402 Lans Road, Beaver Falls PA

Eric Adams, Post Road, Sudbury MA

Hubert Sims, 328A Brook Road, Roanoke VA

Amy Wilde, 334 Bayshore Pkwy, Mountain View CA

Sal Carpenter, 6th Street,boston MA

[[Email protected] sedawk]# sed ' s/ma/, massachusetts/' list

To place a comma between the Boston and the MA, the instruction replaces the spaces in front of the two acronyms with a comma and a space.

There are 3 ways to specify multiple directives on the command line:

1. Separate the directives with semicolons.

   Sed ' s/ma/, massachusetts/; s/pa/, pennsylvania/' list

2. Placing-e,-e before each instruction is a way for SED to recognize script commands.

   Sed-e ' s/ma/, massachusetts/'-e ' s/pa/, pennsylvania/' list

3. Use the branch instruction function of the Bourne shell. A multiple-line input prompt (>) appears when you press return after entering a single quotation mark.

   Sed '

   > s/ma/, massachusetts/

   >s/pa/, pennsylvania/' list

Script file:

It is impractical to enter a longer editing script on the command line. So you need to create a script file to put the SED command. Use-F to specify the name of the script file.

Sed-f scriptfile File

Prevent automatic display of input lines:

The default operation of SED is to output each input line, and-N to prevent automatic output. When you specify-N, to output a line, you need to print the command p.

Sed-n-E ' s/ma/massachusetts/p ' list

Summary of command-line options for SED:

-e Edit subsequent commands

-F Follow the file name in the script

-n block automatic output of input rows

Using awk:

Command-line Syntax:

awk ' instructions ' files

Directives must be enclosed in single quotes to differentiate them from the shell. You can enter multiple command lines in the same way as sed: separate commands with semicolons or use the multi-line input function of the borune shell.

Awk-f script files

Error message:

1. The entire process is not enclosed in curly braces

2. Do not enclose the instruction in single quotes

3. Do not enclose regular expressions in slashes//

Summary of options:

-F Follow Script text name

-F Changing field separators

-V Follow Var=vallue

Use both SED and awk:

[Email protected] sedawk]# vim namestate

s/ca/, california/

s/ma/, massachusetts/

s/ok/, oklahoma/

s/pa/, pennsylvania/

s/va/, virginia/

[Email protected] sedawk]# sed-f namestate list

John Daggett, 341 King Road, Plymouth, Massachusetts

Alice Ford, East Broadway, Richmond, Virginia

Orville Thomas, 11345 Oak Bridge Road, Tulsa, Oklahoma

Terry Kalkas, 402 Lans Road, Beaver Falls, Pennsylvania

Eric Adams, Post Road, Sudbury, Massachusetts

Hubert Sims, 328A Brook Road, Roanoke, Virginia

Amy Wilde, 334 Bayshore Pkwy, Mountain View, California

Sal Carpenter, 6th Street,boston, Massachusetts

[Email protected] sedawk]# sed-f namestate List | Awk-f, ' {print $4} '

Massachusetts

Virginia

Oklahoma

Pennsylvania

Massachusetts

Virginia

California

Massachusetts

Add:

S/regular/complex

Because no address is specified, it affects only the first occurrence on the current line. If regular is not found in the current row, an error occurs. To find multiple occurrences on the same line, you must specify G.

/regular/s/regular/complex/g

This command affects the first line in the file that matches this address. The first regular, is an address, the second is a pattern that matches the replacement command, to apply it to all rows, you must use the global command to place G before the address.

G/regular/s/regular/complex/g

The meaning of G is different, the first G is the global command, which means that all rows that match the address are changed, and the G at the end is a flag that changes all occurrences of the current row.

Sed&&awk Study notes (1)