sed和awk是Linux/Unix系統(tǒng)中強大的文本處理工具，sed用於流式編輯，適合查找替換、刪除插入等操作，awk則是完整的文本處理語言，擅長字段提取、條件過濾和數(shù)據(jù)計算。 1. sed常用功能包括：使用s/old/new/g全局替換文本，3s///在指定行替換，/pattern/s///在匹配行替換，d刪除特定行（如/^$/d刪空行），i和a在指定位置插入或追加文本，-i參數(shù)可保存修改到文件並用-i.bak備份原文件。 2. awk常用功能包括：{print $1,$3}打印指定列，-F','設(shè)置分隔符處理CSV，$2>30按條件過濾行，NR>1跳過頭部，{sum =$2} END{print sum}求和統(tǒng)計，END{print NR}計數(shù)，以及print "Label: "$1格式化輸出。 3. 可通過管道組合二者，如cat log | sed 's/.*] "\(GET|POST\) .*" //' | awk '{print $1}' | sort | uniq -c | sort -nr清洗日誌並統(tǒng)計IP訪問次數(shù)。 4. 使用時應(yīng)避免常見錯誤：用單引號防止shell擴展，sed中可換分隔符如s|old|new|g避免路徑衝突，awk支持變量和編程結(jié)構(gòu)，修改前先預(yù)覽不加-i，注意正則表達式中.和*的特殊含義。掌握sed和awk能顯著提昇文本處理效率，適用於自動化、日誌分析和數(shù)據(jù)清洗，常可替代更複雜的Python或Perl腳本。

sed and awk are two of the most powerful text-processing tools in Linux and Unix-like systems. While they may seem cryptic at first, mastering them can dramatically improve your efficiency when working with text files, logs, configuration files, and data streams. This guide breaks down practical uses of both tools with real-world examples, focusing on day-to-day tasks.

What Are sed and awk ?

• sed (Stream Editor) : Processes text line by line. It's ideal for find-and-replace, inserting or deleting lines, and basic text transformations.
• awk (Named after its creators: Aho, Weinberg, and Kernighan) : A full scripting language for text processing. It excels at working with structured data (like CSVs), extracting fields, and performing calculations.

They're often used together in pipelines to filter, transform, and analyze text efficiently.

Practical Uses of sed

sed works on streams — it reads input, applies edits, and outputs the result. By default, it doesn't modify the original file unless told to.

1. Find and Replace Text

The most common use of sed is replacing text using the s (substitute) command.

 sed 's/old-text/new-text/' filename

Example: Replace all instances of "apple" with "orange" in a file:

 sed 's/apple/orange/' fruits.txt

?? This only replaces the first occurrence per line. To replace all occurrences, add the g (global) flag:

 sed 's/apple/orange/g' fruits.txt

2. Replace on Specific Lines

You can limit substitutions to certain lines.

• Replace only on line 3:

   sed '3s/apple/orange/' fruits.txt

• Replace only in lines containing "fruit":

   sed '/fruit/s/apple/orange/' fruits.txt

3. Delete Lines

Use the d command to remove lines.

• Delete line 5:

   sed '5d' file.txt

• Delete all blank lines:

   sed '/^$/d' file.txt

• Delete lines containing "error":

   sed '/error/d' log.txt

4. Insert or Append Text

• Insert "Header" before line 1:

   sed '1i\Header' file.txt

• Append "Footer" after line 1:

   sed '1a\Footer' file.txt

5. Save Changes to File

By default, sed outputs to stdout. To edit a file in place, use -i :

 sed -i 's/apple/orange/g' fruits.txt

? Use -i.bak to create a backup before editing:

 sed -i.bak 's/apple/orange/g' fruits.txt

Practical Uses of awk

awk treats each line as a record and splits it into fields. By default, fields are separated by whitespace.

1. Print Specific Columns

Print the first and third fields from each line:

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

Useful for log files or CSV-like data.

Example input ( data.txt ):

 John 25 Engineer
Jane 30 Designer
Bob 35 Manager

Command:

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

Output:

 John Engineer
Jane Designer
Bob Manager

2. Use a Custom Field Separator

For CSV files, use -F to define the delimiter:

 awk -F',' '{print $2, $4}' users.csv

For tab-separated files:

 awk -F'\t' '{print $1}' data.tsv

3. Filter Rows Based on Conditions

Print lines where the second field is greater than 30:

 awk '$2 > 30' data.txt

Print lines where the first field is "Jane":

 awk '$1 == "Jane"' data.txt

Combine conditions:

 awk '$2 > 25 && $3 == "Engineer"' data.txt

4. Process Headers and Summarize Data

Skip the header line:

 awk 'NR > 1 {print}' file.csv

NR = Number of Records (line number)

Sum values in a column:

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

Count lines:

 awk 'END {print NR}' file.txt

5. Format Output with Labels

 awk '{print "Name: " $1 ", Age: " $2}' data.txt

Output:

 Name: John, Age: 25
Name: Jane, Age: 30

Combining sed and awk in Pipelines

You can chain both tools for advanced processing.

Example: Clean a log file, extract IP addresses, and count occurrences:

 cat access.log | \
sed 's/.*\] "\(GET\|POST\) .*" //' | \
awk '{print $1}' | \
sort | uniq -c | sort -nr

Breakdown:

• sed : Removes log prefix and HTTP request line
• awk : Extracts first field (IP)
• sort | uniq -c : Counts unique IPs
• Final sort -nr : Sorts by count descending

Common Pitfalls and Tips

• Use single quotes around sed and awk scripts to avoid shell expansion.
• In sed , the delimiter in s/// can be changed (eg, s|old|new|g ) — useful when working with paths.
• awk supports variables, loops, and functions — it's a full scripting language.
• Always test without -i first to preview changes.
• Be cautious with regex — . and * have special meanings.

Final Thoughts

sed and awk are not just legacy tools — they're fast, lightweight, and perfect for automation, log parsing, and data munging. Start with simple substitutions and field extractions, then gradually explore pattern matching, conditions, and arithmetic.

Once you're comfortable, you'll find yourself reaching for them instead of writing longer scripts in Python or Perl — especially in shell pipelines.

Basically, if it involves text, sed and awk can probably help.

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