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system/awk.md

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+# Basics
+
+See a file's contents:
+
+Return full contents of a string:
+
+> awk '{ print }' file
+
+Print the first and second column:
+
+> awk '{print$1$2}'
+
+Return every line with the word 'the' (like grep):
+
+> awk '/the/{print}' file
+
+Print everything containing a lowercase letter:
+
+> awk '/[a-z]/{print}' file
+
+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].
+
+# Conditionals
+
+> awk '{ if($1 ~ /123/) print }' file
+
+Check if the first column is equal to 1 or 2 or 3, and if so then print that line.
+
+Grep for 'hawk' in a story:
+
+> awk '/hawk/' story.txt
+
+Return any line with one or more "&" sequences:
+
+> awk '/&+/' script.sh
+
+The pipe is used for 'or', so 'Orcs or drums' would be:
+
+> awk '/Orcs|Drums/' story.txt
+
+Basic variables are:
+
+- FS = Input field separator
+
+- OFS = Output field separator
+
+- NF = Number of fields on the current line
+
+- NR = Number of records in the current file
+
+- RS = Record separator
+
+- ORS = Output record separator
+
+- FILENAME = the file you're looking at.
+
+So you can count the number of lines in a file, by referencing the number of 'end line' statements:
+
+> awk 'END{print NR}' story.txt
+
+Print line 2 from story.txt
+
+> awk '{if(NR~/^2$/)print}' story.txt
+
+Same, but any line starting with "2":
+
+> awk '{if(NR~/^2/)print}' story.txt
+
+