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Curly braces in sed

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# 1  
Old 06-18-2015
Curly braces in sed
Hi,

I have below command in one of the script. Can you please let me know what does the curly braces do over here \{1,\}. The remaining part of the code atleast I am able to understand.

Code:
sed -n 's/.*\-\([0-9])\{1,\}\)\-.*/\1/p'

# 2  
Old 06-18-2015
Hi, it means 1 or more occurrences of the preceding character or sub-expression, in this case: ), so 1 or more closing parentheses..
# 3  
Old 06-18-2015
Quote:
Originally Posted by tostay2003
Can you please let me know what does the curly braces do over here \{1,\}.
Scrutinizer is right. You can use this device to "multiply" a previous expression, similar to a "*", but with added functionality. For instance:

Code:
X            # matches exactly one single "X"
X*           # matches any number of "X"s, including zero
X\{3\}       # matches exactly 3 "X"s
X\{1,\}      # matches any number of "X"s, from 1 up
X\{,5\}      # matches up to 5 "X"s
X\{3,5\}     # matches 3 to 5 "X"s, hence either "XXX", "XXXX" or "XXXXX"

Notice, that, instead of a single character like "X" here, you can also modify complex expressions with that modifier. For instance:

Code:
|[^|]*          # matches a "field" in tabular, pipe-separated data
                # i.e. "|field1|field2|field3....."
 
\(|[^|]*\)\{3\} # matches 3 such fields

I hope this helps.

bakunin
# 4  
Old 06-18-2015
Code:
sed -n 's/.*\.\([0-9]\{1,\}\)\..*/\1/p'

I had it slightly wrong, but I got the idea of \{1,\}

However when I have the value such as

Code:
echo "testing.123.xyz.456.txt" | sed -n 's/.*\.\([0-9]\{1,\}\)\..*/\1/p'

I am getting value "456" instead of first pattern. Is there anywhere that I am going wrong.
# 5  
Old 06-18-2015
Code:
echo "testing.123.xyz.456.txt" | sed -n 's/.*\.\([0-9]\{1,\}\)\..*/\1/p'

The issue is that the red part of the regex matches the part of the string. The `.*' will try to match as much as it can.

Perhaps, modifying your regex a bit:
Code:
echo "testing.123.xyz.456.txt" | sed -n 's/[^.]*\.\([0-9]\{1,\}\)\..*/\1/p'

[^.]*: keep matching any char that is not a literal period. Stops when it does.
This User Gave Thanks to Aia For This Post:
tostay2003
# 6  
Old 06-18-2015
Or to get the first field with numbers, try:
Code:
sed -n 's/^\([^0-9.].\)*\([0-9]*\).*/\2/p'

or if is always the second field, try:
Code:
cut -d. -f2

Last edited by Scrutinizer; 06-18-2015 at 09:58 AM..
This User Gave Thanks to Scrutinizer For This Post:
tostay2003
# 7  
Old 06-18-2015
Quote:
Originally Posted by Aia
Code:
echo "testing.123.xyz.456.txt" | sed -n 's/.*\.\([0-9]\{1,\}\)\..*/\1/p'

The issue is that the red part of the regex matches the part of the string. The `.*' will try to match as much as it can.

Perhaps, modifying your regex a bit:
Code:
echo "testing.123.xyz.456.txt" | sed -n 's/[^.]*\.\([0-9]\{1,\}\)\..*/\1/p'

[^.]*: keep matching any char that is not a literal period. Stops when it does.
Great.. This works... is ^ in square brackets used as a negation?
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