Can you explain why
This one gives $? = 1
echo "uus" | grep -w -o [0123456789]\*
and this one give $? = 0
echo "-uus" | grep -w -o [0123456789]\*
Can you explain why This one gives $? = 1 echo uus | grep
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Can you explain why
This one gives $? = 1
echo "uus" | grep -w -o [0123456789]\*
and this one give $? = 0
echo "-uus" | grep -w -o [0123456789]\*
Your regular expression can match an empty string. The
-wflag means that any match must be preceded by beginning-of-line or a non-word character, and followed by end-of-line or a non-word character.In the case of
uus, the beginning of line is followed be a word character, sogrepcan’t match an empty string as a word there. The end of line is preceded by a word character, sogrepcan’t match an empty string as a word there.In the case of
-uus, the beginning of line is followed by-, which is a non-word character, sogrepcan match the empty string as a word between the beginning of the line and the-character.