CODEWITHSUNDEEP
regexgrep
Karim Osama
Karim Osama

Reputation: 21

Find the first name that starts with any letter than S using regex

I am new to regex and I am trying to find the last names that only start with S followed by comma and then space and then the first names that doesn't start with S from a text file. I am using the terminal on a MacBook.

This is my regex

^[S\w][,]?[' ']?[A-RT-Z]?

My full command

cat People.txt | grep -E ^[S\w][,]?[' ']?[A-RT-Z]?

The first name is the second word and the last name is the first word on each line.

The results I get:

Schmidt, Paul

Sells, Simon

Smith, Peter

Stephens, Sheila

What I am expecting to get

Schmidt, Paul

Smith, Peter

Upvotes: 0

Views: 657

Answers (2)

Jonathan Leffler
Jonathan Leffler

Reputation: 754520

The first rule of writing regular expressions in a shell script (or at the terminal) is "enclose the regular expression in single quotes" so that the shell doesn't try to interpret the metacharacters in the regex. You might sometimes use double quotes instead of single quotes if you need to match single quotes but not double quotes or if you need to interpolate a variable, but aim to use single quotes. Also, avoid UUoC — Useless Use of cat.

Your question currently shows two regular expressions:

^[S\w][,]?[' ']?[A-RT-Z]?

cat People.txt | grep -E ^[S\w][,]?[' ']?[P\w+]?

If written as suggested, these would become:

grep -E -e '^[Sw],? ?[A-RT-Z]?' People.txt
grep -E -e '^[Sw],? ?[Pw+]?' People.txt

The shell removes the backslashes in your rendition. The + in the character class matches a plus sign. You don't need square brackets around the comma (though they do no major harm). I use the -e option for explicitness, and so I can add extra arguments after the regex (-w or -l or -n or …) when editing commands via history. (I also dislike having options recognized after non-option arguments; I often run with $POSIXLY_CORRECT set in my environment. That's a personal quirk.)

The first of the two commands looks for a line starting S or w, followed by an optional comma, an optional blank, and an optional upper-case letter other than S. The second is similar except that it looks for an optional P or w. None of this bears much relationship to the question.

You need an expression more like one of these:

grep -E -e '^[S][[:alpha:]]*, [^S]' People.txt
grep -E -e '^[S][a-zA-Z]*, [^S]' People.txt

These allow single-character names — just S — but you can use + instead of * to require one or more letters.

There are lots of refinements possible, depending on how much you want to work, but this does the primary job of finding 'first word on the line starts with S, and is followed by a comma, a blank, and the second word does not start with S'.

Given a file People.txt containing:

Randall, Steven
Rogers, Timothy
Schmidt, Paul
Sells, Simon
Smith, Peter
Stephens, Sheila
Titus, Persephone
Williams, Shirley
Someone
S

Your regular expressions produce the output:

Schmidt, Paul
Sells, Simon
Smith, Peter
Stephens, Sheila
Someone
S

My commands produce:

Schmidt, Paul
Smith, Peter

Upvotes: 1

MonkeyZeus
MonkeyZeus

Reputation: 20747

Something like this seems to work fine:

^S.*, [^S].*$
  • ^S.* - must start with S and start capturing everything
  • , [^S] - leading up to a comma, space, not S
  • .*$ - capture the rest of the string

https://regex101.com/r/76bfji/1

Upvotes: 0

Related Questions