sed和awk是Linux中強(qiáng)大的文本處理工具，適用於命令行下的高效文本操作，用於日誌解析、配置文件編輯和數(shù)據(jù)轉(zhuǎn)換。 1. sed用於流編輯，可進(jìn)行文本替換（如s/old/new/替換首次出現(xiàn)，s/old/new/g全局替換），在特定行操作（如3s/old/new/僅第3行，2,5s/old/new/g第2到5行），刪除行（/^$/d刪空行，/error/d刪含error的行），插入或追加文本（/start/i\New line before在匹配前行插入，/end/a\New line after在匹配後行追加），使用-i選項可直接修改文件，建議用其他分隔符如|避免路徑替換時的“slash hell”。 2. awk擅長基於字段的文本處理，基本語法為awk 'pattern { action }' file.txt，默認(rèn)以空白分隔字段，可打印指定字段（{print $1, $3}），使用-F指定分隔符（-F','處理CSV，-F':'處理passwd文件），支持模式過濾（$2 == "active"打印第二字段為active的行，/error/匹配含error的行並打印行號NR），可進(jìn)行計算（{sum = $2} END {print "Total:", sum}求和），添加條件與格式化輸出（$3 > 100 {print $1 " is over budget"}），內(nèi)置變量包括NR（當(dāng)前行號）、NF（當(dāng)前行字段數(shù)）、FILENAME（文件名），如{print NR ". " $0 " (fields: " NF ")"}。 3. sed和awk可結(jié)合使用，通過管道實現(xiàn)複雜處理：先用sed清理文本再awk處理，如sed 's/^\[ \\t\]\*//; s/\[ \\t\]\*$//' file.txt | awk '$2 > 50 {print $1}'去除首尾空白後打印第二字段大於50的第一字段；或awk提取字段後sed追加內(nèi)容，如awk -F'|' '{print $2, $4}' data.txt | sed 's/$/ added/'。 4. 實際應(yīng)用包括：提取日誌中的IP並統(tǒng)計grep -oE '\b([0-9]{1,3}\.){3}[0-9]{1,3}\b' access.log | sort | uniq -c，再用awk '$1 > 100 {print $2}'篩選訪問超100次的IP；安全修改配置文件sed -i.bak 's/^#\(Port 22\)/\1/' /etc/ssh/sshd_config取消註釋Port 22並備份原文件；格式化ps輸出ps aux | awk '$3 > 5.0 {print $1, $2, $3, $11}' | head -10列出CPU使用超5%的前10個進(jìn)程?？傊?，處理文本流時用sed，分析結(jié)構(gòu)化數(shù)據(jù)時用awk，兩者結(jié)合可大幅提升命令行文本處理效率。

sed and awk are two of the most powerful text-processing tools in Linux. They allow you to manipulate text efficiently from the command line, making them essential for log parsing, configuration file editing, and data transformation. Here's how to use them effectively.

1. Using sed for Stream Editing

sed (stream editor) is ideal for performing basic text transformations on an input stream (a file or input from a pipeline).

Common sed Operations

• Substitute text
  Replace the first occurrence of a pattern on each line:

  

   sed 's/old/new/' file.txt

  Replace all occurrences:

   sed 's/old/new/g' file.txt

• Replace on specific lines
  Only replace on line 3:

  

   sed '3s/old/new/' file.txt

  Replace in a range (lines 2 to 5):

   sed '2,5s/old/new/g' file.txt

• Delete lines
  Delete blank lines:

   sed '/^$/d' file.txt

  Delete lines containing a pattern:

   sed '/error/d' file.log

• Insert or append text
  Insert a line before a match:

   sed '/start/i\New line before' file.txt

  Append a line after a match:

   sed '/end/a\New line after' file.txt

• Edit files in place
  Use -i to save changes directly:

   sed -i 's/foo/bar/g' config.txt

? Tip: Use a different delimiter (like | ) to avoid "slash hell" when working with paths:

 sed 's|/home/user|/tmp|g' file.txt

2. Using awk for Field-Based Text Processing

awk excels at processing structured text (like CSV or log files), where data is organized in fields.

Basic awk Syntax

 awk 'pattern { action }' file.txt

• Print specific fields
  By default, fields are separated by whitespace. Print the first and third fields:

   awk '{print $1, $3}' data.txt

• Use a custom delimiter
  For comma-separated values:

   awk -F',' '{print $2}' users.csv

  Or with a colon (eg, /etc/passwd ):

   awk -F':' '{print $1, $6}' /etc/passwd

• Filter lines with patterns
  Print lines where the second field equals "active":

   awk '$2 == "active" {print $0}' status.txt

  Print lines containing the word "error":

   awk '/error/ {print NR, $0}' app.log

• Perform calculations
  Sum values in the second column:

   awk '{sum = $2} END {print "Total:", sum}' numbers.txt

• Add conditions and formatting

   awk '$3 > 100 {print $1 " is over budget"}' expenses.txt

• Built-in variables

  • NR – Current record (line) number
  • NF – Number of fields in the current line
  • FILENAME – Name of the input file

  Example:

   awk '{print NR ". " $0 " (fields: " NF ")"}' data.txt

3. Combining sed and awk

You can pipe sed and awk together for advanced processing:

• Clean up text with sed , then process with awk :

   sed 's/^[ \t]*//; s/[ \t]*$//' file.txt | awk '$2 > 50 {print $1}'

  (Removes leading/trailing whitespace, then prints first field if second field > 50)

• Extract and reformat data:

   awk -F'|' '{print $2, $4}' data.txt | sed 's/$/ added/'

  (Prints fields 2 and 4, then appends " added" to each line)

4. Practical Examples

• Extract IPs from a log and count occurrences:

   grep -oE '\b([0-9]{1,3}\.){3}[0-9]{1,3}\b' access.log | sort | uniq -c

  Then use awk to filter suspicious ones:

   awk '$1 > 100 {print $2}' # IPs accessed more than 100 times

• Modify configuration files safely:

   sed -i.bak 's/^#\(Port 22\)/\1/' /etc/ssh/sshd_config

  (Uncomments "Port 22" and creates a backup)

• Format output from ps :

   ps aux | awk '$3 > 5.0 {print $1, $2, $3, $11}' | head -10

  (Lists top 10 processes with CPU > 5%)

Both tools are scriptable and can handle complex logic, but for quick command-line text manipulation, even simple one-liners save a lot of time. Start with basic substitutions and field printing, then build up as needed.

Basically, if you're editing text streams — use sed . If you're analyzing or reporting on structured data — reach for awk .

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