Malin Freeborn
ba8026e0c3
input examples are now given as ```bash input $ARG1 ``` While outputs use md's '> ' sign as a quote.
90 lines
1.5 KiB
Markdown
90 lines
1.5 KiB
Markdown
---
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title: "awk"
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tags: [ "Documentation", "System" ]
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---
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# Basics
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See a file's contents:
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Return full contents of a string:
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```bash
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awk '{ print }' file
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```
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Print the first and second column:
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```bash
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awk '{print$1$2}'
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```
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Return every line with the word 'the' (like grep):
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```bash
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awk '/the/{print}' file
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```
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Print everything containing a lowercase letter:
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```bash
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awk '/[a-z]/{print}' file
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```
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Same with numbers [0-9], or using a caret we can show lines starting with a number - ^[0-9], or ending with an uppercase letter - $[A-Z].
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# Conditionals
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```bash
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awk '{ if($1 ~ /123/) print }' file
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```
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Check if the first column is equal to 1 or 2 or 3, and if so then print that line.
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Grep for 'hawk' in a story:
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```bash
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awk '/hawk/' story.txt
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```
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Return any line with one or more "&" sequences:
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```bash
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awk '/&+/' script.sh
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```
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The pipe is used for 'or', so 'Orcs or drums' would be:
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```bash
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awk '/Orcs|Drums/' story.txt
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```
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Basic variables are:
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- FS = Input field separator
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- OFS = Output field separator
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- NF = Number of fields on the current line
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- NR = Number of records in the current file
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- RS = Record separator
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- ORS = Output record separator
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- FILENAME = the file you're looking at.
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So you can count the number of lines in a file, by referencing the number of 'end line' statements:
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> awk 'END{print NR}' story.txt
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Print line 2 from story.txt
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> awk '{if(NR~/^2$/)print}' story.txt
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Same, but any line starting with "2":
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> awk '{if(NR~/^2/)print}' story.txt
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