Update cheatsheets

while

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+---
+syntax: markdown
+tags: [tldr, common]
+source: https://github.com/tldr-pages/tldr.git
+---
+# while
+
+> Simple shell loop.
+> More information: <https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_09_04_09>.
+
+- Read `stdin` and perform an action on every line:
+
+`while read line; do echo "$line"; done`
+
+- Execute a command forever once every second:
+
+`while :; do {{command}}; sleep 1; done`