Add IO_getenv, IO_setenv, IO_unsetenv

CHANGES

@@ -2,6 +2,7 @@ This file describes changes in the IO package.
 
 X.Y.Z (YYYY-MM-DD)
   - Change minimal required GAP version to 4.11
+  - Add IO_getenv, IO_setenv, IO_unsetenv
 
 4.7.3 (2022-09-25)
   - Fix a build issue where running `make clean` would break the build

doc/main.xml

@@ -130,6 +130,7 @@ The following functions from the C library are made available as
 <C>fork</C>,
 <C>fstat</C>,
 <C>getcwd</C>,
+<C>getenv</C>,
 <C>gethostbyname</C>,
 <C>gethostname</C>,
 <C>getpid</C>,
@@ -165,12 +166,14 @@ The following functions from the C library are made available as
 <C>select</C>,
 <C>send</C>,
 <C>sendto</C>,
+<C>setenv</C>,
 <C>setsockopt</C>,
 <C>socket</C>,
 <C>stat</C>,
 <C>symlink</C>,
 <C>telldir</C>,
 <C>unlink</C>,
+<C>unsetenv</C>,
 <C>write</C>. <P/>
 
 Use the <C>man</C> command in your shell to get information about these
@@ -501,6 +504,17 @@ For details see <Q><C>man 3 getcwd</C></Q>.
 </Description>
 </ManSection>
 
+<ManSection>
+<Func Name="IO_getenv" Arg="name"
+      Comm="Return the value of an environment variable."/>
+<Returns> a string or <K>fail</K> </Returns>
+<Description>
+Return the current value of the environment variable <A>name</A>.
+If the variable is not in the current environment, <C>fail</C> is returned.
+For details see <Q><C>man 3 getenv</C></Q>.
+</Description>
+</ManSection>
+
 <ManSection>
 <Func Name="IO_gethostbyname" Arg="name"
       Comm="Return host information by name."/>
@@ -898,6 +912,17 @@ that no 7th argument is necessary.
 </Description>
 </ManSection>
 
+<ManSection>
+<Func Name="IO_setenv" Arg="name, value, overvwrite"
+      Comm="Set the value of an environment variable."/>
+<Returns> <K>true</K> or <K>fail</K> </Returns>
+<Description>
+Set the current value of the environment variable <A>name</A> to <A>value</A>
+if it has either not been set before, or <A>overwrite</A> is <C>true</C>.
+For details see <Q><C>man 3 setenv</C></Q>.
+</Description>
+</ManSection>
+
 <ManSection>
 <Func Name="IO_setsockopt" Arg="fd, level, optname, optval"
       Comm="Sets a socket option."/>
@@ -965,6 +990,16 @@ For details see <Q><C>man 2 unlink</C></Q>.
 </Description>
 </ManSection>
 
+<ManSection>
+<Func Name="IO_unsetenv" Arg="name"
+      Comm="Remove an environment variable."/>
+<Returns> <K>true</K> or <K>fail</K> </Returns>
+<Description>
+Remove the environment variable <A>name</A>.
+For details see <Q><C>man 3 unsetenv</C></Q>.
+</Description>
+</ManSection>
+
 <ManSection>
 <Func Name="IO_WaitPid" Arg="pid, wait"
       Comm="Waits for the termination of a child process."/>

src/io.c

@@ -1863,6 +1863,49 @@ static Obj FuncIO_gethostname(Obj self)
 }
 #endif
 
+static Obj FuncIO_getenv(Obj self, Obj name)
+{
+    if (!IS_STRING_REP(name)) {
+        SyClearErrorNo();
+        return Fail;
+    }
+    char * res = getenv(CONST_CSTR_STRING(name));
+    if (res == NULL) {
+        SySetErrorNo();
+        return Fail;
+    }
+    return MakeString(res);
+}
+
+static Obj FuncIO_setenv(Obj self, Obj name, Obj value, Obj overwrite)
+{
+    if (!IS_STRING_REP(name) || !IS_STRING_REP(value) ||
+        (overwrite != True && overwrite != False)) {
+        SyClearErrorNo();
+        return Fail;
+    }
+    int res = setenv(CONST_CSTR_STRING(name), CONST_CSTR_STRING(value),
+                     overwrite == True);
+    if (res < 0) {
+        SySetErrorNo();
+        return Fail;
+    }
+    return True;
+}
+
+static Obj FuncIO_unsetenv(Obj self, Obj name)
+{
+    if (!IS_STRING_REP(name)) {
+        SyClearErrorNo();
+        return Fail;
+    }
+    int res = unsetenv(CONST_CSTR_STRING(name));
+    if (res < 0) {
+        SySetErrorNo();
+        return Fail;
+    }
+    return True;
+}
 
 //
 // list of functions to export
@@ -2104,6 +2147,10 @@ static StructGVarFunc GVarFuncs[] = {
     GVAR_FUNC(IO_gethostname, 0, ""),
 #endif
 
+    GVAR_FUNC(IO_getenv, 1, "name"),
+    GVAR_FUNC(IO_setenv, 3, "name, value, overwrite"),
+    GVAR_FUNC(IO_unsetenv, 1, "name"),
+
     { 0 }
 
 };

tst/all.tst

@@ -86,6 +86,10 @@ fail
 gap> IsString(IO_getcwd());
 true
 
+# IO_getenv(name)
+gap> IO_getenv(fail);
+fail
+
 # IO_gethostbyname(name)
 gap> IO_gethostbyname(fail);
 fail
@@ -239,6 +243,10 @@ fail
 gap> IO_sendto(fail, fail, fail, fail, fail, fail);
 fail
 
+# IO_setenv(name, value, overwrite)
+gap> IO_setenv(fail, fail, fail);
+fail
+
 # IO_setsockopt(fd, level, optname, optval)
 gap> IO_setsockopt(fail, fail, fail, fail);
 fail
@@ -262,6 +270,10 @@ gap> #IO_telldir(); # TODO: test this
 gap> IO_unlink(fail);
 fail
 
+# IO_unsetenv(name)
+gap> IO_unsetenv(fail);
+fail
+
 # IO_WaitPid(pid, wait)
 gap> IO_WaitPid(fail, fail);
 fail

tst/funcs.tst

@@ -36,3 +36,29 @@ gap> r:=IO_lstat(".");; IsRecord(r); Set(RecNames(r));
 true
 [ "atime", "blksize", "blocks", "ctime", "dev", "gid", "ino", "mode", 
   "mtime", "nlink", "rdev", "size", "uid" ]
+
+#
+gap> env:=RecNames(GAPInfo.SystemEnvironment)[1];;
+gap> IO_getenv(env) = GAPInfo.SystemEnvironment.(env);
+true
+
+# find an environment variable name hopefully not yet set
+gap> env := Concatenation("GAP_IO_TEST_VAR_", String(Random(10^15,10^16-1)));;
+gap> IO_getenv(env);
+fail
+gap> IO_setenv(env, "A", true);
+true
+gap> IO_getenv(env);
+"A"
+gap> IO_setenv(env, "B", false);
+true
+gap> IO_getenv(env);
+"A"
+gap> IO_setenv(env, "B", true);
+true
+gap> IO_getenv(env);
+"B"
+gap> IO_unsetenv(env);
+true
+gap> IO_getenv(env);
+fail