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1.1 root 1: .\" @(#)ae4 6.1 (Berkeley) 5/22/86
2: .\"
3: .NH
4: GLOBAL COMMANDS
5: .PP
6: The global commands
7: .UL g
8: and
9: .UL v
10: are used to perform one or more editing commands on all lines that either
11: contain
12: .UL g ) (
13: or don't contain
14: .UL v ) (
15: a specified pattern.
16: .PP
17: As the simplest example, the command
18: .P1
19: g/UNIX/p
20: .P2
21: prints all lines that contain the word `UNIX'.
22: The pattern that goes between the slashes can be anything
23: that could be used in a line search or in a substitute command;
24: exactly the same rules and limitations apply.
25: .PP
26: As another example, then,
27: .P1
28: g/^\*e\*./p
29: .P2
30: prints all the formatting commands in a file (lines that begin with `\*.').
31: .PP
32: The
33: .UL v
34: command is identical to
35: .UL g ,
36: except that it operates on those line that do
37: .ul
38: not
39: contain an occurrence of the pattern.
40: (Don't look too hard for mnemonic significance to
41: the letter `v'.)
42: So
43: .P1
44: v/^\*e\*./p
45: .P2
46: prints all the lines that don't begin with `\*.' _
47: the actual text lines.
48: .PP
49: The command that follows
50: .UL g
51: or
52: .UL v
53: can be anything:
54: .P1
55: g/^\*e\*./d
56: .P2
57: deletes all lines that begin with `\*.',
58: and
59: .P1
60: g/^$/d
61: .P2
62: deletes all empty lines.
63: .PP
64: Probably the most useful command that can follow a global is the
65: substitute command, for this can be used to make a change
66: and print each affected line for verification.
67: For example, we could change the word `Unix' to `UNIX'
68: everywhere, and verify that
69: it really worked,
70: with
71: .P1
72: g/Unix/s//UNIX/gp
73: .P2
74: Notice that we used `//' in the substitute command to mean
75: `the previous pattern', in this case, `Unix'.
76: The
77: .UL p
78: command is done on every line
79: that matches the pattern,
80: not just those on which a substitution took place.
81: .PP
82: The global command operates by making
83: two passes over the file.
84: On the first pass, all lines that match the pattern are marked.
85: On the second pass, each marked line in turn is examined,
86: dot is set to that line, and the command executed.
87: This means that it is possible for the command that follows a
88: .UL g
89: or
90: .UL v
91: to use addresses, set dot, and so on, quite freely.
92: .P1
93: g/^\*e\*.PP/+
94: .P2
95: prints the line that follows each `.PP' command (the signal for
96: a new paragraph in some formatting packages).
97: Remember that `+' means `one line past dot'.
98: And
99: .P1
100: g/topic/?^\*e\*.SH?1
101: .P2
102: searches for each line that contains `topic', scans backwards until it finds
103: a line that begins `.SH' (a section heading) and prints the line
104: that follows that,
105: thus showing the section headings under which `topic' is mentioned.
106: Finally,
107: .P1
108: g/^\*e\*.EQ/+,/^\*e\*.EN/-p
109: .P2
110: prints all the lines that lie between
111: lines beginning with `.EQ' and `.EN' formatting commands.
112: .PP
113: The
114: .UL g
115: and
116: .UL v
117: commands can also be
118: preceded by line numbers, in which case the lines searched
119: are only those in the range specified.
120: .SH
121: Multi-line Global Commands
122: .PP
123: It is possible to do more than one command under the control of a
124: global command, although the syntax for expressing the operation
125: is not especially natural or pleasant.
126: As an example,
127: suppose the task is to change `x' to `y' and `a' to `b' on all lines
128: that contain `thing'.
129: Then
130: .P1
131: g/thing/s/x/y/\*e
132: s/a/b/
133: .P2
134: is sufficient.
135: The `\*e' signals the
136: .UL g
137: command that the set of commands continues on the next line;
138: it terminates on the first line that does not end with `\*e'.
139: (As a minor blemish, you can't use a substitute command
140: to insert a newline within a
141: .UL g
142: command.)
143: .PP
144: You should watch out for this problem:
145: the command
146: .P1
147: g/x/s//y/\*e
148: s/a/b/
149: .P2
150: does
151: .ul
152: not
153: work as you expect.
154: The remembered pattern is the last pattern that was actually
155: executed,
156: so sometimes it will be
157: `x' (as expected), and sometimes it will be `a'
158: (not expected).
159: You must spell it out, like this:
160: .P1
161: g/x/s/x/y/\*e
162: s/a/b/
163: .P2
164: .PP
165: It is also possible to execute
166: .UL a ,
167: .UL c
168: and
169: .UL i
170: commands under a global command; as with other multi-line constructions,
171: all that is needed is to add a `\*e' at the end of each line except the last.
172: Thus to add a `.nf' and `.sp' command before each `.EQ' line, type
173: .P1
174: g/^\*e\*.EQ/i\*e
175: \&\*.nf\*e
176: \&\*.sp
177: .P2
178: There is no need for a final line containing a
179: `\*.' to terminate the
180: .UL i
181: command,
182: unless there are further commands
183: being done under the global.
184: On the other hand, it does no harm to put it in either.
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